Elements of the atmosphere

Correct answer: C, visibility may decrease. A high concentration of dust particles scatters sunlight and makes the air hazy, so distant objects become harder to see. Dust does not permanently stop rainfall or remove nitrogen from the air.

Nitrogen makes up about 78% of dry air and oxygen about 21%; together they account for roughly 99% of the atmosphere by volume. This is why these two gases form most of the air. They do not by themselves form the ozone layer or a dust layer, and their combined share is certainly not a very small part. Hence option B is correct.

Correct answer: D, ozone. Ozone in the stratosphere absorbs much of the Sun’s harmful ultraviolet radiation, reducing the amount that reaches Earth’s surface. Oxygen helps form ozone, but ozone is the main absorber asked for here.

Correct answer: B, respiration. In aerobic respiration, cells use oxygen to release energy from food; carbon dioxide and water are produced during the complete process. Plants generally take in carbon dioxide, not oxygen, as a raw material for photosynthesis. Oxygen itself is not a condensation nucleus, and ozone is chiefly responsible for absorbing harmful ultraviolet radiation in the atmosphere.

Correct answer: C. Atmospheric aerosols are tiny solid particles or liquid droplets suspended in air. Dust, smoke particles and sea-salt particles are examples. Large rocks, oceans and river valleys are not airborne particles.

Nitrogen makes up about 78% of dry air and is comparatively unreactive under ordinary atmospheric conditions. Its large, stable presence helps maintain the overall composition of the atmosphere and dilutes highly reactive gases. It does not convert all water vapour into rain, remove ozone completely, or cover the Sun; those statements confuse nitrogen with unrelated atmospheric processes.

B is correct. During photosynthesis, plants use carbon dioxide from the air and water, using light energy, to make glucose. Oxygen is released as a by-product. Argon and ozone are not the carbon-containing raw material used to build glucose.

C is correct. In dry air, nitrogen is the most abundant gas and oxygen is second; argon is third at about 0.93% by volume. Water vapour is excluded from dry air and varies considerably, while carbon dioxide and ozone occur in much smaller proportions.

Water vapour is a variable atmospheric element that strongly influences weather. When moist air rises and cools, water vapour can condense into clouds and later produce rain or snow; it also affects humidity and heat transfer. Magma, lava and granite are geological materials rather than normal atmospheric elements, so they do not explain ordinary weather formation.

Nitrogen and oxygen are the two principal gases of Earth’s dry atmosphere. Nitrogen forms about 78% and oxygen about 21%, so option A is the most correct pair. Argon is also present in a smaller proportion. Carbon dioxide, ozone, methane, and water vapour occur in much smaller or variable quantities, while hydrogen and helium are only trace constituents near Earth’s surface.

Ozone absorbs a substantial part of the Sun’s harmful ultraviolet radiation, especially in the stratospheric ozone layer. This absorption protects living organisms from excessive UV exposure, making option B correct. Argon is an inert gas with a small atmospheric share, dust mainly scatters or absorbs some light near the surface, and nitrogen is abundant but is not the principal atmospheric absorber referred to here.

Water vapour is called a variable atmospheric element because its amount changes greatly with location, season, temperature and weather conditions. It may be abundant in humid air and scarce in dry air. Nitrogen, oxygen and argon are comparatively stable major constituents of dry air, so they are not the best answer to this question about variability.

The correct answer is B, water vapour. When moist air cools, some water vapour condenses into tiny droplets or ice crystals, forming clouds. Droplets that grow large enough can fall as rain, while a cloud near the ground is called fog.

The governing concept is the water cycle and phase change. Before rain develops, water is present in the atmosphere as invisible water vapour, a gas. Cooling causes this vapour to condense around suitable nuclei into cloud droplets; droplets then combine and fall as rain when sufficiently large. Thus option A is correct. Dust can provide nuclei, while argon and nitrogen remain atmospheric gases but do not become raindrops.

The correct answer is B, gases, water vapour, and dust particles. The atmosphere consists mainly of gases and also contains variable water vapour and tiny suspended particles such as dust. The other groups name landforms, water bodies, or geological events and materials, not atmospheric components.

The correct answer is A, nitrogen. By volume, dry air is approximately 78% nitrogen and 21% oxygen; argon makes up about 0.93%, while carbon dioxide is present in a much smaller, variable amount. Nitrogen therefore has the largest proportion.

The correct answer is B, oxygen. In dry air, nitrogen is the most abundant gas at about 78% by volume, followed by oxygen at about 21%. Argon is about 0.93%, and carbon dioxide is present in a much smaller, variable amount. Thus oxygen ranks second by proportion.

The correct answer is C, water vapour. It is a variable component of the atmosphere and is central to humidity, cloud formation, and precipitation. When moist air cools, water vapour can condense into cloud droplets or ice crystals. Changes in water’s state also transfer latent heat, which can affect atmospheric circulation and storms. Water vapour is itself a gas; the question distinguishes it from the major permanent gases such as nitrogen and oxygen.

The correct answer is B, aerosols. Aerosols are tiny solid particles or liquid droplets suspended in a gas such as air; dust, smoke, and fine sea-salt particles are examples. Water vapour is water in gaseous form, while ozone and nitrogen are gases, not general names for suspended particles.

The correct answer is B, CO₂. The formula has one carbon atom (C) and two oxygen atoms (O₂), which is the composition of a carbon dioxide molecule.

Argon is an element whose internationally accepted chemical symbol is Ar, so option C is correct. The first letter of an element symbol is capitalised and the second letter, when present, is lowercase. N₂ denotes nitrogen molecules, O₃ denotes ozone, and CO₂ denotes carbon dioxide. These are chemical formulae for other substances, not the symbol of argon.

The correct answer is D. Water vapour is a variable component of the atmosphere: evaporation adds it to the air, while condensation and precipitation remove it. Its amount therefore changes from place to place and over time; it is not constant or greater than nitrogen.

Evaporation changes liquid water at the surface into invisible water vapour, which enters the atmosphere and increases its moisture content. This process occurs over oceans, lakes, rivers, soil and wet vegetation. Nitrogen and argon are relatively stable gases, while ozone is produced mainly through photochemical reactions involving oxygen and ultraviolet radiation. Hence, option A is correct.

The correct answer is C, carbon dioxide. In photosynthesis, plants use carbon from carbon dioxide and water, together with light energy, to make sugars such as glucose. Oxygen is released as a by-product. Plants also need nitrogen for growth, but they generally obtain usable nitrogen compounds through their roots rather than taking nitrogen gas directly from the air.

The correct answer is D, oxygen. In aerobic respiration, cells use oxygen in reactions that release usable energy from food molecules such as glucose. Carbon dioxide and water are commonly produced. Not all organisms depend on oxygen, but it is the gas used in aerobic respiration.