Elements of the atmosphere

Correct answer: A. Nitrogen is more abundant, and oxygen is used directly in respiration

Correct answer: A. Dry air contains about 78% nitrogen and 21% oxygen, so nitrogen is more abundant. Humans and many other organisms use oxygen directly in aerobic respiration. Thus A correctly compares both their relative amounts and their role in respiration.

Correct answer: B. Carbon dioxide — photosynthesis

Correct answer: B. Plants take in carbon dioxide and use it, together with water and light energy, to make glucose during photosynthesis; they also release oxygen. Ozone, rather than nitrogen, is the gas commonly associated with absorbing harmful ultraviolet radiation in the atmosphere.

Correct answer: B. Nitrogen, oxygen, argon, carbon dioxide

Correct answer: B. In dry air, nitrogen makes up about 78% and oxygen about 21%. Argon is present in a much smaller proportion, while carbon dioxide is present in a trace amount. Therefore, the decreasing order is nitrogen, oxygen, argon, then carbon dioxide.

Correct answer: A. Nitrogen is permanent and water vapour is variable

The correct answer is A. Nitrogen is classified as a permanent gas because its proportion in the atmosphere is relatively stable. Water vapour is variable because its amount changes with location, weather and season. Dust and clouds are not permanent gases.

Correct answer: A. Aerosols

The correct answer is A, aerosols. Aerosols are tiny solid particles or liquid droplets dispersed and suspended in air. Smoke and industrial emissions can contain suspended particles such as soot and dust, so these particles are atmospheric aerosols.

Correct answer: A. Respiration and combustion

The correct answer is A. Many organisms need oxygen for aerobic respiration, which releases usable energy from food. Oxygen also supports ordinary combustion, so a major decrease would make many fires harder to sustain. Tides and Earth’s orbit are not directly controlled by atmospheric oxygen.

Correct answer: A. Water vapour — evaporation from oceans and surface water

Option A is correct because evaporation from oceans, lakes, rivers, soil, and other surface-water bodies is a major way water vapour enters the atmosphere. Transpiration from plants also contributes. Sea spray mainly introduces salt particles and aerosols, not argon. Atmospheric nitrogen is not supplied by dust particles, and ozone is formed mainly through photochemical reactions involving oxygen under ultraviolet radiation, not from river water. Thus the source-element relationship in A is the valid one.

Correct answer: A. Nitrogen is more abundant than oxygen

The correct answer is A. Near Earth’s surface, dry air contains about 78% nitrogen and 21% oxygen by volume, so nitrogen is more abundant. These are approximate values; water vapour is excluded because its amount varies. Argon is about 0.93%, and carbon dioxide is far less abundant than oxygen.

Correct answer: A. Visibility can decrease as more sunlight is scattered.

Answer: A. Dust particles suspended in air scatter sunlight. If their concentration is high, the air can become hazy and visibility can decrease. The effect depends on the particles and local conditions; dust does not make nitrogen disappear or cause atmospheric pressure to vanish.

Correct answer: A. Major gases, variable water vapour, and fine particles

The atmosphere is a mixture containing major gases such as nitrogen and oxygen, smaller amounts of argon and carbon dioxide, variable water vapour, and suspended particles such as dust, smoke, salt, and pollen. This complete description makes option A correct. Rocks, metals, water, and lava may occur in particular Earth environments, but they are not the complete composition of the atmosphere. Nitrogen alone is also insufficient.

Correct answer: A. Carbon dioxide

The correct answer is A, carbon dioxide. Plants use carbon dioxide in photosynthesis to make sugars. Humans produce it during cellular respiration and release it when they exhale.

Correct answer: A. Its amount varies greatly

The correct answer is A. Water-vapour content varies with place, time and weather. Excluding it lets dry-air percentages describe the relatively stable proportions of gases such as nitrogen and oxygen on a consistent basis.

Correct answer: D. Ozone is O₃ and ordinary oxygen is O₂

The correct answer is D. An ordinary oxygen molecule contains two oxygen atoms, so its formula is O₂. An ozone molecule contains three oxygen atoms, so its formula is O₃. These different molecular structures give the two forms different properties.

Correct answer: D. They scatter light and obstruct its path

The correct answer is D. Dust and smoke contain particles suspended in the air. These particles scatter light in different directions and can obstruct some of the light coming from distant objects. This reduces contrast, making distant objects look hazy or unclear.

Correct answer: A. Nitrogen is the more abundant and comparatively less reactive gas, while oxygen is directly used in respiration.

The correct answer is A. Nitrogen makes up about 78% of dry air, while oxygen makes up about 21%. Nitrogen is comparatively unreactive under ordinary conditions, whereas oxygen is directly used in aerobic respiration and also supports combustion. Nitrogen is still important to life, but organisms generally use it after it has been converted into usable compounds.

Correct answer: C. Plants use it in photosynthesis.

The correct answer is C. Plants and other photosynthetic organisms take in carbon dioxide and use it, together with water and light energy, to make sugars during photosynthesis. The carbon becomes part of organic matter and can pass through food chains. Carbon dioxide does not form the ozone layer, whose molecules are made of O₃.

Correct answer: A. Because its amount is relatively stable and it is chemically inert

The correct answer is A. Argon is a noble gas that reacts very little under ordinary conditions, so its proportion in the atmosphere remains relatively stable. Water vapour, by contrast, varies considerably with location and weather.

Correct answer: D. Nitrogen, oxygen, argon, carbon dioxide

The correct answer is D: nitrogen, oxygen, argon, then carbon dioxide. Decreasing order means going from the greatest proportion to the smallest. Dry air is about 78% nitrogen and 21% oxygen; argon is just under 1%, and carbon dioxide is present in a much smaller amount. Thus nitrogen comes first, followed by oxygen, argon, and carbon dioxide.

Correct answer: B. Oxygen, O₂

The correct answer is B. Ordinary molecular oxygen is diatomic: each molecule contains two oxygen atoms, so its formula is O₂. Ozone is O₃, nitrogen gas is N₂, and argon is represented by Ar.

Correct answer: B. Smoke from vehicles and industries

The correct answer is B. Smoke from vehicles and industries contains fine particles and droplets released by human activities, making it a source of human-made aerosols. Sea-spray salt is generally a natural aerosol, while nitrogen and water vapour are gases rather than suspended particles or droplets.

Correct answer: C. Volcanic ash

The correct answer is C, volcanic ash. A natural aerosol consists of fine solid particles or liquid droplets suspended in air that come from a natural process. Volcanic eruptions release fine ash into the atmosphere. Factory and vehicle smoke and construction dust are generally associated with human activities.

Correct answer: A. Green plants use carbon dioxide in photosynthesis, and humans and most animals take in oxygen for respiration

The correct answer is A. Green plants use carbon dioxide, water and light energy to make food during photosynthesis, releasing oxygen. Humans and most animals use oxygen in cellular respiration and release carbon dioxide. This is a broad exchange between plants and animals; plants also respire, and the statement does not describe every living organism.

Correct answer: C. CO₂ — Ozone

The correct answer is C. CO₂ is carbon dioxide, not ozone; ozone has the formula O₃. The other matches are correct: N₂ is nitrogen, O₂ is oxygen, and Ar is the chemical symbol for argon.

Correct answer: C. Dust particles

Option C is correct because dust particles are tiny solid substances suspended in the atmosphere, not gases. They are important despite their small size: they can scatter sunlight, reduce visibility, and provide surfaces on which water vapour condenses during cloud formation. Nitrogen, oxygen, and carbon dioxide are gaseous components of air under ordinary atmospheric conditions. The governing concept is that the atmosphere contains both gases and suspended particulate matter, often called aerosols.

Correct answer: A. It consists mainly of nitrogen, with other gases, water vapour and fine particles also present

D is incorrect; A is correct. The atmosphere is a mixture of gases, including abundant nitrogen and oxygen, as well as smaller amounts of other gases. It also contains variable water vapour and suspended particles such as dust. The amounts of water vapour and particles can vary by place and weather conditions.