Hydrological cycle

Correct answer: A. Topographic highs called watershed divides

Explanation: A drainage basin collects surface water that flows toward a common river, lake, or outlet. Its boundary is mainly a topographic divide: water falling on opposite sides of a high ridge can flow into different drainage systems. The other options do not define this landform boundary.

Correct answer: A. They can temporarily store excess water and delay its release

Explanation: A lake can temporarily hold some incoming water and release it over a longer period. This can delay and spread the flow reaching the downstream river, lowering its peak discharge. The effect depends on the lake’s capacity, water level, and outlet; it is not guaranteed in every situation.

Correct answer: A. Fertiliser chemicals carried into rivers by runoff

Explanation: Runoff from fertilised fields can carry dissolved nutrients, including nitrates and phosphates, into rivers and streams. This human-caused input can degrade water quality and may promote excessive algal growth. The other examples describe natural processes rather than a direct human source of water pollution.

Correct answer: A. Strong surface runoff and low vegetation cover

Explanation: The governing concept is that soil erosion increases when flowing water has high energy and the soil surface is poorly protected. Intense rainfall can produce rapid surface runoff, especially where vegetation cover is sparse. Plant roots normally bind soil particles, while leaves and litter reduce the direct impact of raindrops; without this protection, particles are detached and transported downslope. Therefore, option A is correct because it combines strong runoff with weak vegetation protection. Gentle rain and dense grass in option B generally reduce detachment and slow the flow. Flat land with high infiltration in option C encourages water to enter the soil rather than travel across it, while a stable lake with little flow in option D is not an active erosion setting. The process is thus linked to runoff energy, slope, soil exposure, and vegetation cover.

Correct answer: A. Lower infiltration and higher surface runoff

Explanation: The governing concept is the relationship between soil pore space, infiltration, and runoff. Clay has very fine particles and small pores, and compaction reduces the connected spaces through which water can move downward. Consequently, rainfall enters the ground slowly. If rainfall intensity is greater than this limited infiltration capacity, water accumulates on the surface and flows away as runoff. Therefore, option A is correct: compacted clayey soil generally has lower infiltration and greater surface runoff. Option B reverses the expected effect and incorrectly claims zero runoff. Options C and D are unrelated exaggerations; soil texture does not automatically stop rainfall or create an ocean. The actual result can also depend on slope, rainfall intensity, surface cover, and cracks, but among the choices A is the only scientifically appropriate answer.

Correct answer: A. Saturation limit decreases as temperature falls

Explanation: The governing concept is the temperature dependence of saturation vapour pressure. Warm air can contain more water vapour before reaching saturation because its higher temperature allows more water molecules to remain in the gaseous state. When air cools, the saturation limit falls. If the actual vapour content remains high while the limit decreases, relative humidity rises and the air may reach the dew point; further cooling then promotes condensation into droplets, clouds, fog, or dew. Thus, option A is correct. Option B is false because cold air still contains gases, including water vapour. Options C and D are also incorrect: cold air is not confined to oceans and does not turn into salt. The statement concerns capacity at saturation, not the complete absence of vapour in cold air.

Correct answer: A. Baseflow may decrease

Explanation: Baseflow is the relatively steady contribution of groundwater to a stream or river, especially during periods without rainfall. Excessive pumping lowers the groundwater table and can reduce the hydraulic connection between the aquifer and the river. With less groundwater discharging into the channel, the river’s dry-season flow may decline, and some small streams can become intermittent or even dry. Therefore, option A is correct. The size of the effect depends on pumping intensity, aquifer properties, recharge, distance from the river, and local geology. Salinity may increase in some coastal or special settings, but it is not inevitable or instantly produced, so option B is too absolute. Options C and D violate basic river-flow and water-cycle principles: pumping does not reverse river direction or guarantee increased rainfall.

Correct answer: A. They can carry moisture to large areas and cause rainfall

Explanation: Monsoon winds are seasonally reversing air movements that strongly influence the transfer of water vapour between ocean and land. During the rainy season, winds commonly move from relatively warm oceanic regions toward heated land, carrying moist air inland. When this air rises because of convection, mountains, or convergence, it cools; condensation then forms clouds and may produce widespread rainfall. Therefore, option A is correct. The amount and distribution of rain also depend on sea-surface temperature, pressure patterns, relief, wind direction, and the duration of the monsoon. Option B is incorrect because winds do not stop Earth’s rotation. Option C confuses transport of water vapour with removal of dissolved ocean salts, and option D incorrectly suggests a direct underground-to-cloud pump. Monsoons mainly transport atmospheric moisture and organize seasonal precipitation.

Correct answer: A. Meltwater from land ice can flow into the oceans

Explanation: Glaciers on land store water outside the oceans. When they melt, some of that water flows through rivers or directly into the sea, adding water to the oceans and contributing to a long-term rise in average global sea level. This differs from melting floating sea ice, which has little direct effect on sea level because it already displaces seawater.

Correct answer: A. The timing and amount of flow may be regulated

Explanation: A reservoir can temporarily store water and release it later. This can change when and how much water reaches the river downstream. The effect depends on how the reservoir is operated; it does not mean that the river always runs dry or that rainfall stops.

Correct answer: A. Because atmospheric circulation, relief, and moisture sources vary

Explanation: Rainfall depends partly on how atmospheric circulation transports moisture, on the availability of moisture sources, and on relief. For example, mountains can force moist air to rise and produce more precipitation on a windward slope, while other areas may receive less. These factors make rainfall vary from place to place.

Correct answer: A. Moist air rising over a mountain and cooling

Explanation: When moist air is forced up a mountain slope, it expands and cools as air pressure decreases with height. If it cools enough to reach saturation, water vapour condenses into clouds and precipitation may form, commonly on the windward side. This is orographic rainfall.

Correct answer: A. They affect interception, infiltration, and transpiration

Explanation: Forest canopies intercept some rainfall, and roots and leaf litter can help water infiltrate into the soil rather than run off rapidly. Trees also return water vapour to the atmosphere through transpiration. These processes influence local water storage and movement, although their effects vary with local conditions.

Correct answer: A. Slower, with a less intense peak flow

Explanation: Lakes, marshes, and forest soils can temporarily store water, while vegetation and permeable ground can slow runoff and encourage infiltration. This may delay water reaching river channels and reduce the peak flow. It does not prevent all floods: prolonged or intense rain can exceed the available storage.

Correct answer: A. Most dissolved salts remain in the sea during evaporation.

Explanation: During evaporation, water molecules enter the atmosphere as vapour while most dissolved salts remain in the sea. The vapour can cool and condense into cloud droplets, which may later fall as relatively fresh rain or snow. Therefore option A is correct; seawater is saline, but its salts do not generally evaporate with the water.

Correct answer: A. Formation of cloud droplets from water vapour may become more difficult.

Explanation: Condensation nuclei are tiny particles, such as dust or sea-salt aerosols, on whose surfaces water vapour can condense. If suitable nuclei are scarce, droplet formation may be less efficient or require greater supersaturation. Thus cloud-droplet formation can become more difficult, making option A correct. Nuclei help condensation; they do not create water.

Correct answer: A. Condensation

Explanation: The dew point is the temperature at which air with a given moisture content becomes saturated. If it cools to that point, water vapour can condense into tiny liquid droplets or ice crystals, often on condensation nuclei. This is condensation, so option A is correct. Percolation is the downward movement of water through soil, while groundwater extraction and tides are different processes.

Correct answer: A. Toward the oceans through surface runoff and groundwater flow.

Explanation: Over the long term, precipitation in many land areas exceeds the water returned by evapotranspiration. The surplus can flow over the surface into streams and rivers, or infiltrate and move as groundwater; these routes eventually carry much of it toward the oceans. Temporary storage can delay this movement. Therefore option A is correct.

Correct answer: A. Infiltration is water entering the soil; percolation is its further downward movement through the ground.

Explanation: Infiltration is the entry of water from the ground surface into the soil through pores and cracks. After entering, water may move farther downward through soil and underlying material; this movement is called percolation. The usual sequence is therefore entry into the soil followed by deeper downward movement, as option A states.

Correct answer: A. Groundwater slowly flows into the river channel.

Explanation: Baseflow is the part of river discharge supplied by delayed pathways, especially groundwater seeping into the channel. This slow supply can maintain some river flow between rainfall events, including during dry weather. It does not guarantee that a river will flow indefinitely, since drought or groundwater depletion can reduce baseflow. Therefore option A is correct.

Correct answer: A. Extraction exceeds recharge

Explanation: The governing concept is the balance between groundwater recharge and groundwater extraction. Recharge adds water to an aquifer through rainfall infiltration, seepage, and other forms of subsurface entry, whereas extraction removes water through wells, pumps, and springs. If withdrawal remains greater than recharge over time, the amount of stored groundwater decreases and the water table falls. Therefore, option A is correct. Options B, C, and D describe situations in which water input is greater or infiltration is strong, so they would generally support a stable or rising groundwater level rather than a decline. Local geology and seasonal variation may modify the rate, but the basic balance remains decisive.

Correct answer: A. They regulate storage and timing of water release

Explanation: The governing concept is human regulation of water storage and river discharge. A dam creates a reservoir that temporarily holds part of the water that would otherwise move downstream. Operators may release this stored water at selected times for irrigation, drinking water, hydropower, flood management, or environmental purposes. This changes the natural timing and sometimes the seasonal amount of river flow, so option A is correct. A dam does not make evaporation impossible; exposed reservoir water can evaporate. It cannot transform rainfall into sea salt, and it does not automatically remove a watershed divide. Its principal hydrological effect is controlled storage and release.

Correct answer: A. It stores water for long periods and releases it slowly on melting

Explanation: The governing concept is storage and delayed release within the hydrological cycle. Glaciers retain precipitation as snow and ice for months, years, or much longer, instead of allowing all of it to become immediate runoff. When temperatures rise, melting releases water gradually into streams and rivers, often supporting downstream flow during a particular season. Thus option A is correct. Glacier storage can delay the movement of water from the atmosphere and land to rivers and oceans, although the exact amount and timing depend on temperature, snowfall, glacier size, and melt rate. It does not remove ocean salinity, permanently eliminate clouds, or invariably reduce groundwater to zero.

Correct answer: A. It transports oceanic moisture to land and causes precipitation

Explanation: The governing concept is atmospheric transport of water vapour between ocean and land. During a monsoon, seasonal pressure and wind changes help move moist air from a warmer ocean toward land. As this air rises because of heating, topography, or convergence, it cools and water vapour condenses into clouds, producing rainfall. Therefore, option A correctly describes the monsoon contribution to the hydrological cycle. The strength and distribution of rainfall vary with sea-surface conditions, pressure patterns, relief, and the season. Monsoon winds do not boil groundwater, stop ocean tides, or create clouds from salt; those statements confuse different physical processes.

Correct answer: A. Evaporation absorbs heat and condensation releases heat

Explanation: The governing concept is the reversible energy exchange called latent heat. During evaporation, liquid water changes into vapour and requires energy to separate its molecules; that energy is absorbed from the surrounding surface or air, often producing a cooling effect. During condensation, water vapour changes back into liquid, and the previously stored energy is released to the surrounding atmosphere. Hence option A is correct. The same amount of energy is involved for the reverse phase changes under comparable conditions, though the observed weather effect depends on where the energy is transferred. Option B reverses or oversimplifies the effects, C denies the energy relation, and D reverses both processes.