2021 HKDSE 地理 模擬試題連答案詳解

Granite forms from magma cooling slowly beneath the Earth's surface (intrusive / plutonic), resulting in coarse crystals. Basalt forms from lava cooling quickly on the surface (extrusive / volcanic), resulting in fine-grained crystals. Thus, statement (1) is correct, statement (2) is correct, and statement (3) is incorrect because granite cools from magma beneath the surface, not from lava on the surface.

Award 1 mark for option A. Statements (1) and (2) are correct; (3) is incorrect.

Due to wave refraction along irregular coastlines, waves bend as they enter shallower water near headlands first. Wave orthogonals (lines showing the direction of wave energy propagation) converge on headlands, concentrating energy and causing intensive erosion (forming cliffs, caves, stacks). In bays, water is deeper for longer, causing orthogonals to diverge, dissipating energy and leading to deposition of sediment to form bay-head beaches. All three statements are correct.

Award 1 mark for option D. All three statements (1), (2), and (3) are correct descriptions of wave refraction.

In tropical rainforests, dense evergreen vegetation forms the largest nutrient store (biomass). The hot and wet climate promotes rapid chemical decomposition of leaf litter by bacteria and fungi. However, the soil nutrient store is small and poor in available mineral nutrients due to rapid uptake by dense roots and intense leaching caused by heavy rainfall. Hence, statement (3) is incorrect while (1) and (2) are correct.

Award 1 mark for option A. Statements (1) and (2) are correct; (3) is incorrect.

Drip irrigation delivers water directly to crop root zones at slow rates, minimising evaporation losses and surface runoff. By avoiding waterlogging and excessive rising of the water table, it mitigates the capillary rise of mineral salts, thereby reducing soil salinisation. However, drip irrigation systems require capital investment for pipes, emitters, filters, and pumps, making statement (3) incorrect.

Award 1 mark for option A. Statements (1) and (2) are correct; (3) is incorrect.

A footloose industry is one whose location is not significantly restricted by access to raw materials or raw markets because its inputs and finished products are typically lightweight, compact, and of high unit value (e.g., microelectronics, software development), and transport costs make up a very small percentage of total production costs.

Award 1 mark for option C. Options A, B, and D describe weight-losing or heavy bulk manufacturing industries.

While carbon dioxide has a baseline GWP of 1, methane has a GWP of approximately 28–36, nitrous oxide has a GWP around 265–298, and CFCs (synthetic halocarbons) have GWPs ranging from thousands to over 10,000 times that of carbon dioxide due to their high infrared absorbance and long atmospheric lifetimes.

Award 1 mark for option D. CFCs have the highest GWP per molecule among the choices listed.

Ventilation corridors allow cooler sea breezes or regional winds to penetrate the urban core, dispersing trapped heat. Green roofs and vertical greening provide shade and cooling via evapotranspiration. High-albedo materials reflect incoming solar radiation rather than absorbing and re-radiating it as sensible heat. All three measures effectively mitigate the urban heat island effect.

Award 1 mark for option D. All three statements (1), (2), and (3) are effective UHI mitigation strategies.

Stratified sampling divides the study area into distinct sub-groups or strata (in this case, different functional/land-use zones such as commercial, residential, and recreational) and ensures that samples are drawn proportionally or representatively from each zone, making it the most suitable method for comparing variations among differing functional zones.

Award 1 mark for option B. Stratified sampling allows representative sampling across predefined distinct zones.

Statement (1) is correct: systematic sampling along a transect across different land use types captures spatial variation effectively.
Statement (2) is correct: stratified sampling across contrasting urban morphologies (e.g. street canyons vs open park) ensures representativeness across environments.
Statement (3) is incorrect: deliberately excluding unshaded stations creates systematic bias and prevents an accurate comparison between different microclimatic conditions.

A (1 mark): Award 1 mark for the correct option A. No mark for other options.

Statement (1) is correct: intrusive igneous rocks (e.g. granite) cool slowly beneath the Earth's surface within magma chambers, allowing large mineral crystals to grow.
Statement (2) is correct: granitic rocks are felsic/acidic rocks rich in silicate minerals like quartz and feldspar.
Statement (3) is incorrect: pyroclastic fallout forms extrusive rocks (such as tuff or volcanic ash deposits), not intrusive rocks.

A (1 mark): Award 1 mark for the correct option A. No mark for other options.

As waves approach an irregular coastline, wave refraction causes wave energy (and orthogonals) to converge on headlands where water becomes shallow first, leading to concentrated wave attack and intense erosion. In sheltered bays, wave rays diverge and wave energy spreads out, allowing deposition of sediments to occur. Thus, statement (1) is reversed/incorrect, while statements (2) and (3) are correct.

C (1 mark): Award 1 mark for the correct option C. No mark for other options.

All three statements correctly explain the winter monsoon mechanism:
(1) Intense cooling of the landmass leads to the formation of the Siberian High.
(2) Air moves down the pressure gradient from the cold continent toward the warmer oceanic low-pressure belts.
(3) The Coriolis force deflects moving air to the right in the Northern Hemisphere, turning northerly winds into northeasterly monsoons.

D (1 mark): Award 1 mark for the correct option D. No mark for other options.

Comparison (1) is incorrect because traditional iron and steel is heavy and raw-material weight-losing (high weight loss), whereas high-tech manufacturing produces lightweight, high-value components with low weight loss.
Comparisons (2) and (3) are correct: high-tech relies on skilled scientific labor and agglomerates near research institutions, universities, and air-transport hubs, rather than being bound to heavy bulky raw materials.

C (1 mark): Award 1 mark for the correct option C. No mark for other options.

Statement (1) is correct: high biodiversity and luxuriant vegetation store the vast majority of nutrients in living biomass.
Statement (2) is incorrect: tropical rainforest soils (oxisols/latosols) are heavily leached by high rainfall and are nutrient-poor, meaning the soil store is relatively small.
Statement (3) is correct: high temperatures and high moisture all year round accelerate decomposer activity and weathering, enabling rapid uptake and cycling of nutrients.

B (1 mark): Award 1 mark for the correct option B. No mark for other options.

Statements (1) and (2) are effective: air ventilation corridors promote natural wind penetration to carry away trapped anthropogenic heat, and green roofs/walls increase evapotranspiration cooling while lowering surface temperatures.
Statement (3) is incorrect: low-albedo dark surfaces absorb more solar radiation and re-radiate it as sensible heat, worsening the urban heat island effect. High-albedo (reflective/cool) surfaces should be used instead.

A (1 mark): Award 1 mark for the correct option A. No mark for other options.

Mechanisms (1) and (2) are positive feedback loops: melting ice lowers albedo (more heat absorbed -> more melting), and warming oceans release dissolved \(\text{CO}_2\) (strengthening the greenhouse effect -> further warming).
Mechanism (3) describes a negative feedback loop: increased reflection by low clouds reduces solar energy reaching the surface, thereby counteracting and moderating the temperature increase.

A (1 mark): Award 1 mark for the correct option A. No mark for other options.

Wave refraction occurs as wave crests approach an irregular coastline. As waves enter shallower water near headlands first, they slow down due to friction with the seabed, while the parts of the wave travelling through deeper water in bays continue at higher speeds. This bends the wave crests toward the headlands. Consequently, wave orthogonals converge on headlands, concentrating wave energy and promoting erosional landforms (statement 2 is correct). In contrast, orthogonals diverge in bays, dispersing wave energy and facilitating the deposition of sediment to form bayhead beaches (statement 1 is correct). Over time, this refraction causes wave crests to align nearly parallel to the coastline contours (statement 3 is correct). Therefore, (1), (2), and (3) are all correct.

Award 1 mark for D. Deduct 0 marks for incorrect choices.

In a tropical rainforest ecosystem: (1) Biomass is by far the largest nutrient store because of the dense, multi-layered vegetation structure and high living mass. The litter store is kept very small due to year-round high temperatures and high moisture, which promote rapid decomposition by decomposers (statement 1 is incorrect). (2) Nutrient uptake by plants is very rapid due to shallow, extensive root systems and mycorrhizal fungi that quickly absorb released nutrients before they are leached away (statement 2 is correct). (3) The warm and humid climate accelerates deep chemical weathering of the underlying parent rock, providing an ongoing mineral input to the soil nutrient pool (statement 3 is correct). Thus, (2) and (3) only are correct.

Award 1 mark for C. Deduct 0 marks for incorrect choices.

High-technology industries benefit from agglomeration economies: (1) Science and technology parks provide shared infrastructure, high-speed telecommunications, technical support, and conference facilities (statement 1 is correct). (2) Close spatial proximity encourages knowledge spillovers, informal communication, and collaborative research and development between firms and academic institutions (statement 2 is correct). (3) High-tech manufacturing utilizes lightweight, compact microelectronic components with high value-to-weight ratios; it is not a heavy, bulk-material-oriented industry, so raw material freight costs are not a major factor (statement 3 is incorrect). Therefore, (1) and (2) only are correct.

Award 1 mark for A. Deduct 0 marks for incorrect choices.

At oceanic divergent plate boundaries (such as the Mid-Atlantic Ridge): (1) Upwelling magma originating directly from the upper mantle is basic/basaltic, containing low silica and gas levels, which gives it low viscosity and results in effusive lava flows (statement 1 is correct). (2) Violent pyroclastic flows and steep composite cones (stratovolcanoes) are typical of convergent plate boundaries where subduction generates viscous, intermediate-to-acidic (andesitic/rhyolitic) magma with high gas content (statement 2 is incorrect). (3) The tectonic plates pull apart along the boundary, creating rift valleys and extensive mid-ocean ridges where magma escapes through submarine fissures (statement 3 is correct). Therefore, (1) and (3) only are correct.

Award 1 mark for B. Deduct 0 marks for incorrect choices.

(a) (i) Island Arc M is located along a convergent plate boundary where two oceanic plates collide. The denser and older oceanic plate subducts beneath the less dense oceanic plate into the asthenosphere along a subduction zone, creating a deep oceanic trench. As the slab sinks along the Benioff zone, high temperatures and pressure, combined with the release of trapped water/volatiles from ocean floor sediments, lower the melting point of the overlying mantle wedge (flux melting). Partial melting produces andesitic/dacitic magma. Because the magma is less dense than the surrounding mantle and crustal rock, it rises buoyantly through fractures in the overriding plate, erupting onto the sea floor. Over repeated eruptions, volcanic edifices build up above sea level to form a linear/curved chain of volcanic islands known as an island arc.

(ii) Magma at subduction zone stratovolcanoes is typically intermediate to felsic (andesitic to rhyolitic) with high silica content (>60%). High silica content makes the magma highly viscous, trapping large quantities of dissolved gases (such as water vapor, carbon dioxide, sulfur dioxide). As the magma ascends towards the surface, depressurization causes dissolved gases to rapidly expand. The viscous magma prevents gas bubbles from escaping freely, resulting in extreme internal gas pressure build-up until it shatters violently into pyroclasts, ash, and tephra upon explosive release.

(b) Lahars: Explosive eruptions deposit vast volumes of loose, unconsolidated pyroclastic material and ash on steep volcanic slopes. Heavy monsoon rainfall or rapid melting of crater ice/snow mixes with this loose tephra, creating dense, fast-moving volcanic mudflows (lahars) that travel down river valleys, burying coastal settlements.
Tsunamis: Large-scale flank collapse, caldera collapse, or high-volume pyroclastic flows plunging into the ocean displace immense volumes of seawater instantly, generating destructive tsunami waves that propagate rapidly across coastal zones.

(c) Arguments supporting the view (Monitoring & mapping reduce risk):
- Real-time seismic and gas emissions monitoring detects magma ascent early, providing critical warning lead time for organized evacuation.
- Hazard mapping defines exclusion zones, restricting development in high-risk river valleys and coastal zones prone to lahars and pyroclastic density currents.

Counter-arguments / Constraints (Why they are insufficient alone):
- Sudden, rapid-onset explosive events (e.g., Event 3 with only 6 hours lead time) may outpace evacuation logistics.
- Socio-economic factors: Dense coastal populations, farmland dependence on fertile volcanic soils, and lack of alternative livelihood options cause residents to resist evacuation or encroach into exclusion zones.
- Infrastructure and institutional capacity: In less developed regions, poor evacuation roads, inadequate transport, and unreliable communication networks hinder rapid response regardless of early warnings.
- Unpredictability of secondary hazards: Rain-triggered lahars can occur months or years after an eruption during typhoons, long after official alerts end.
Conclusion: Monitoring and mapping are essential but must be paired with public education, drills, adequate emergency shelters, alternative economic support, and resilient transport infrastructure to minimize mortality.

(a) (i) [Max 5 marks]
- Oceanic-oceanic convergent boundary / subduction identified (1)
- Sinking of denser oceanic plate into asthenosphere / trench formation (1)
- Introduction of volatiles / water lowering mantle melting point (flux melting) (1)
- Buoyant ascent of magma through fractures of overriding plate (1)
- Repeated accumulation of eruptive materials building volcanic island arc above sea level (1)

(ii) [Max 3 marks]
- Intermediate to high silica content (andesitic/felsic) (1)
- High viscosity of magma preventing smooth flow (1)
- High concentration of trapped dissolved gases building immense internal pressure prior to explosive release (1)

(b) [Max 4 marks]
- Lahar formation: loose volcanic ash/pyroclasts on steep slopes + heavy torrential rain/crater water mix into slurry (2)
- Tsunami generation: massive pyroclastic flow entering sea / caldera collapse / submarine slope failure displacing water column (2)

(c) [Max 6 marks: 5-6 marks for comprehensive, balanced discussion with explicit reference to data/geographic concepts; 3-4 marks for adequate discussion; 1-2 marks for superficial points]
- Valid points on utility of real-time monitoring and hazard zoning (2)
- Limitations/human factors: population pressure, fertile soil attraction, evacuation bottlenecks, false alarms, poverty, unpredictable magnitude/timing (2)
- Clear judgment/stance supported by logical reasoning and geographical context (2)

(a) 1. Severe annual water deficit: Annual potential evapotranspiration (2150 mm) vastly exceeds annual precipitation (280 mm), creating a perennial soil moisture deficit throughout the year.
2. Highly seasonal and unreliable rainfall: Over 64% of annual rain falls within just two months (July-August), leaving a 10-month-long dry season which severely restricts the natural growing season without artificial water supply.
3. High temperatures: Mean annual temperature is high (27.4°C), accelerating evaporation rates from soil surfaces and transpiration from crops, causing rapid desiccation.

(b) 1. High water use efficiency via drip irrigation: Drip irrigation delivers water directly to crop root zones in precise, controlled amounts, minimizing evaporation losses and avoiding wasteful surface runoff.
2. Microclimate control in greenhouses: Enclosed structures protect crops from excessive solar radiation, high ambient temperatures, and desiccating winds, thereby reducing potential evapotranspiration.
3. Year-round cultivation: Artificial supply of water and nutrients (fertigation) decouples crop growth from seasonal rainfall dependence, allowing multi-cropping and drastically higher yields.

(c) (i) 1. Soil salinization: In semi-arid climates with extreme evaporation, excessive irrigation water draws dissolved mineral salts upward through capillary action. When water evaporates at the surface, salts accumulate in the topsoil, causing soil toxicity and loss of arable land.
2. Groundwater depletion / Land subsidence: Heavy extraction of fossil or deep groundwater exceeding natural recharge rates leads to a lowering of the water table, dried-up wells, and land subsidence.

(ii) Arguments supporting high-tech farming:
- Drastically higher crop yield (85 t/ha vs 1.2 t/ha) and water productivity allow high output in water-scarce lands.
- Insulates crops against climate extremes and rainfall variability, stabilizing food output.

Arguments highlighting limitations for smallholders:
- High capital cost: Initial installation ($45,000/ha) and high operating costs ($6,200/ha) are unaffordable for impoverished smallholder farmers without heavy subsidies or microcredit.
- Technical knowledge and maintenance: High-tech sensors, automated drip lines, and greenhouse repairs require technical expertise and electricity/energy supply that are often absent in rural developing regions.
- Focus on commercial export cash crops rather than local staple food security: High-value crops (e.g., tomatoes/peppers) are sold to affluent urban/export markets, which may not directly address local calorie deficiencies.
- Alternative low-cost appropriate technologies (e.g., zai pits, stone bunds, drought-resistant indigenous crop varieties, rainwater harvesting) are far more accessible, cost-effective, and ecologically resilient for smallholder adoption.
Conclusion: While high-tech farming is technically effective for commercial enterprises, it is not universally the most viable strategy for resource-poor smallholder farmers without accessible financing and appropriate scale adaptation.

(a) [Max 4 marks]
- High potential evapotranspiration relative to low precipitation / severe water deficit (1)
- Quoting relevant data from Fig 2a (2150 mm vs 280 mm / 27.4°C) (1)
- Highly concentrated/brief rainy season (July-August) resulting in prolonged dry season (1)
- High temperature accelerating evaporation and crop transpiration (1)

(b) [Max 4 marks]
- Drip irrigation delivers water directly to root zone / minimizes water loss through evaporation/runoff (2)
- Greenhouse regulates temperature/humidity / shields against intense radiation and wind, lowering transpiration rates (2)

(c) (i) [Max 4 marks, 2 marks per problem with elaboration]
- Soil salinization: capillary rise of salts due to strong evaporation + crust formation (2)
- Groundwater depletion / lowering of water table / saline water intrusion due to over-extraction (2)

(ii) [Max 6 marks: 5-6 marks for comprehensive, two-sided evaluation with clear geographic reasoning; 3-4 marks for competent explanation of pros and cons; 1-2 marks for superficial/one-sided answer]
- Merits of high-tech farming: high water efficiency, climate resilience, high yields (2)
- Constraints for smallholders: exorbitant capital/maintenance costs, reliance on external inputs/electricity, focus on cash crops rather than staple food crops (2)
- Evaluation of appropriate/low-cost alternatives (e.g., rainwater harvesting, zai pits, agroforestry) and overall conclusion (2)

This 12-mark essay question is divided into two distinct components:

1. Explanation component (6 marks):
- Focus on specific mechanisms of biotechnology (GM crops, drought/saline tolerance, shorter growing cycles) and modern irrigation techniques (drip/micro-irrigation, high water-use efficiency, soil protection) that tackle climatic and water constraints in drought-prone environments.

2. Discussion / Evaluation component (6 marks):
- Evaluate the extent to which technology alone can solve famine.
- Balance the benefits of technology (yield enhancement, climate resilience) against non-technological drivers of famine (poverty, inequitable distribution, poor governance, war/displacement, infrastructural inadequacy, dependency, environmental drawbacks).
- Reach a clear, reasoned, and justified conclusion.

Part 1: Explain how biotechnology and modern irrigation methods can help improve agricultural productivity in drought-prone regions (Max. 6 marks)
- Performance Levels:
* 5–6 marks: Comprehensive knowledge and systematic explanation of how both biotechnology (e.g. drought resistance, shorter maturation) and modern irrigation (e.g. drip irrigation, water efficiency) overcome water/climatic constraints to raise productivity.
* 3–4 marks: Adequate knowledge; explains either biotechnology or irrigation in good detail, or both in moderate detail with relevant geographical terminology.
* 1–2 marks: Elementary understanding; brief or superficial listing of technologies without explaining the underlying mechanisms.

Part 2: Discuss whether adopting agricultural technologies is a panacea for combating famines in less developed countries (Max. 6 marks)
- Performance Levels:
* 5–6 marks: Coherent, in-depth discussion presenting a balanced evaluation; clearly evaluates the strengths of technology alongside institutional, economic, political, and ecological barriers; provides a clear, well-supported conclusion.
* 3–4 marks: Sound discussion examining both pros and cons, but arguments may lack depth or focus predominantly on one perspective; offers a reasonable conclusion.
* 1–2 marks: Superficial or one-sided answer; merely lists problems of less developed countries with minimal evaluation of the 'panacea' claim.

(a) (i)
- Travel time decreased for both modes: road-based bus travel time dropped from 58 minutes to 44 minutes (a reduction of 14 minutes or ~24%), and private car travel time decreased from 48 minutes to 38 minutes (a reduction of 10 minutes or ~21%).
- Daily passenger volume declined significantly for buses from 125,000 to 62,000 trips (~50.4% reduction), while private car volume showed a moderate drop from 45,000 to 36,000 trips (20% reduction), with the majority of diverted trips captured by the new MRT rail system (110,000 trips).

(ii)
- Modal Shift / Traffic Diversion: A large volume of commuters shifted from road-based transport (buses and cars) to the rail network (capturing 110,000 daily trips), drastically lowering the overall vehicular density on the corridor.
- Alleviation of Road Congestion: Fewer private vehicles and reduced bus dispatch frequencies reduced bottleneck congestion along main arterial highways linking Town K to the CBD.
- Increased Operating Speeds: Reduced friction and traffic queues allowed bus fleet operating speeds to increase from 18 km/h to 26 km/h.
- Reduced Dwell Time at Stops: Lower passenger boarding volumes (load factor dropping from 92% to 68%) shortened queuing and passenger boarding/alighting times at intermediate stops.
- Smoother Traffic Flow: Clearer road space facilitated faster turnaround times, directly shortening total journey time.

(b) (i)
- Lower Carbon Footprint: The MRT generates only 16 g \(CO_2\) per passenger-km compared to 45 g for buses and 142 g for private cars, significantly mitigating greenhouse gas emissions and urban air pollutants (e.g., \(NO_x\), \(PM_{10}\)).
- High Spatial / Land Efficiency: MRT operates on segregated underground or elevated tracks, requiring 0.0 \(m^2\) of surface road space per passenger, whereas private cars consume 18.5 \(m^2\) per person; this frees up scarce urban surface space.
- High Carrying Capacity: MRT carries huge volumes (110,000 daily trips with an 88% peak load factor), moving mass populations efficiently without clogging surface transit corridors.
- Enhanced Road Safety: Rail transport is far safer with an accident rate of only 0.02 incidents per million passenger-km versus 4.8 for private cars.

(ii)
- Point-to-point Flexibility: Private cars provide door-to-door direct transit without the need for transfers, first-mile/last-mile feeder connections, or fixed timetable scheduling.
- Comfort and Privacy: Higher personal comfort, privacy, status perception, and guaranteed personal space compared to crowded rail carriages during peak hours (88% MRT load factor).
- Travel Needs & Multi-destination Trips: Carrying luggage/goods, travelling with family/dependents, or having irregular routes and off-peak travel schedules that are poorly served by fixed rail alignments.

(c)
- Opportunities:
* TOD integrates high-density residential and commercial land uses around MRT nodes, shortening travel distances and promoting walking/cycling ('first/last-mile' connectivity).
* Electronic road pricing (ERP) directly internalises traffic congestion costs, suppressing unnecessary private vehicular demand and encouraging further modal shift to public transport.
* Revenue from road pricing can cross-subsidise green transit infrastructure improvements.
- Constraints / Challenges:
* Existing built-up suburban fabric: Land resumption and redevelopment around established suburban stations face high financial costs, property rights resistance, and lengthy planning processes.
* Equity and Public Acceptance: Congestion charges may be seen as a regressive tax penalising suburban residents who lack immediate direct access to rapid transit.
* Route / Capacity Strain: Higher localized density around stations may overwhelm station concourses, train capacity, and local feeder road networks during peak hours.

(a) (i) [Max. 2 marks]
- Accurate description of changes in travel time for bus and car (1 mark)
- Accurate description of changes in passenger volume with quantification (1 mark)

(a) (ii) [Max. 5 marks]
- Diversion of commuters to MRT leading to reduced vehicular volume on roads (1 mark)
- Reduction of traffic congestion / bottlenecks along the corridor (1 mark)
- Increase in average operating speed due to smoother road traffic flow (1 mark)
- Decrease in passenger boarding/alighting dwell times at bus stops (1 mark)
- Comprehensive explanation connecting reduced traffic friction to shortened journey time (1 mark)

(b) (i) [Max. 4 marks]
- Explanation of lower emissions / decarbonisation with data citation (1 mark)
- Explanation of road space efficiency / high carrying capacity on segregated track (1 mark)
- Energy efficiency and reduction of urban roadside air pollution (1 mark)
- Higher safety / lower accident rates (1 mark)

(b) (ii) [Max. 3 marks]
- Door-to-door convenience / flexibility without interchange penalty (1 mark)
- Superior comfort, privacy, and personal space compared to crowded peak rail (1 mark)
- Specific journey purposes (e.g. multi-stop chaining, carrying goods, special passenger needs) (1 mark)

(c) [Max. 4 marks]
- Level 3 (4 marks): Comprehensive and balanced discussion demonstrating in-depth knowledge of both opportunities (TOD land synergy, ERP demand management) and constraints (land resumption hurdles, public resistance/equity, infrastructural capacity); logical arguments with sound geographical terminology.
- Level 2 (2-3 marks): Adequate discussion covering both pros and cons, but with limited depth or slight imbalance; reasonable application of transport planning concepts.
- Level 1 (1 mark): Brief, one-sided, or superficial points without structured analysis.

Part 1: Differences in Physical Characteristics and Formation Processes (6 marks)
• Intrusive Igneous Rocks (e.g., Granite):
- Formation: Formed from magma cooling slowly beneath the Earth's surface under high pressure, allowing large crystals to develop over long periods.
- Physical Characteristics: Coarse-grained, phaneritic texture with interlocking crystals of quartz, feldspar, and mica; dense and relatively homogeneous; widely spaced orthogonal joints.
• Extrusive Igneous Rocks (e.g., Volcanic Tuff / Rhyolite):
- Formation: Formed from rapid cooling and solidification of lava or consolidation of pyroclastic materials (volcanic ash and fragments) ejected onto the Earth's surface during volcanic eruptions.
- Physical Characteristics: Fine-grained (aphanitic) or pyroclastic/fragmental texture; crystals are tiny or microscopic; commonly exhibits columnar jointing, flow banding, or vesicular textures.

Part 2: Influence of Rock Structure and Climatic Conditions on Chemical Weathering (6 marks)
• Role of Rock Structure:
- Joints, fractures, and fault lines act as planes of weakness and channels through which subsurface water and dissolved acids percolate deep into the bedrock.
- Closely spaced joints increase the total exposed surface area per unit volume, speeding up chemical reactions.
- Orthogonal jointing in granite allows weathering to attack corners and edges, promoting spheroidal weathering and corestone development.
• Role of Climatic Conditions:
- Hong Kong experiences a humid subtropical monsoon climate with high mean annual temperatures (~23°C) and heavy precipitation (>2,400 mm annually).
- High temperature accelerates the rate of chemical reactions (Van 't Hoff's rule / kinetics of hydrolysis and oxidation).
- Abundant rainfall provides a constant supply of percolating groundwater rich in dissolved organic acids and carbon dioxide (carbonation/acid hydrolysis).
• Discussion / Evaluation:
- Chemical weathering depth in Hong Kong is among the deepest (up to 30–50 metres of regolith) because optimal climatic factors and pervasive jointing work synergistically. Without joints, water cannot penetrate deep into impermeable unweathered rock; without a warm, humid climate, jointed rock would weather primarily through mechanical processes.

Marking Guidelines:

Part 1: Differences between intrusive and extrusive igneous rocks (Max. 6 marks)
• Performance of Candidates:
- 5–6 marks: Comprehensive knowledge and systematic explanation of formation environments (subsurface vs. surface), cooling rates (slow vs. rapid), and resulting textures/crystal characteristics (coarse-grained/phaneritic vs. fine-grained/pyroclastic) with reference to Hong Kong rock examples (granite and tuff/rhyolite).
- 3–4 marks: Adequate explanation of the differences in formation processes and rock textures, but lacks detailed descriptions of specific mineral/textural characteristics or examples.
- 1–2 marks: Elementary descriptions of rocks with vague or confused explanation of formation processes.

Part 2: Influence of rock structure and climatic conditions on chemical weathering (Max. 6 marks)
• Performance of Candidates:
- 5–6 marks: Clear, balanced, and in-depth discussion explaining how structural weaknesses (joint sets, faults, surface area) and climatic variables (temperature, rainfall, soil moisture) interact to dictate the rate, processes (e.g., hydrolysis, oxidation, spheroidal weathering), and regolith depth in Hong Kong.
- 3–4 marks: Adequate discussion mentioning both rock structure and climatic factors, but explanation of specific chemical weathering mechanisms or their interaction is brief or slightly unbalanced.
- 1–2 marks: Superficial listing of climate or rock structure with little understanding of chemical weathering processes.