The question asks for the primary reason behind the increase in atmospheric carbon dioxide over recent decades. This is a fundamental concept in environmental science and climate change. We need to identify the human activity that contributes the most to COâ‚‚ emissions.
A) Burning of fossil fuels. The combustion of coal, oil, and natural gas for energy production, transportation, and industrial processes releases vast quantities of carbon dioxide that has been stored underground for millions of years. This activity is the dominant human-caused factor driving the increase in atmospheric COâ‚‚ concentrations observed over the last century, especially in recent decades.
The question asks about the location of the ozone layer in Earth's atmosphere. To answer this, we need to recall the different layers of the atmosphere and the characteristic features of each layer, specifically where ozone concentration is highest.
Correct Option: C) Between 10 and 50 km. This range accurately describes the altitude of the stratosphere, where the ozone layer is predominantly found and performs its crucial function of absorbing harmful UV radiation.
The question asks about the primary function of the ozone layer. We need to recall the role of the ozone layer in Earth's atmosphere and evaluate each option based on this knowledge.
Correct Option: B) It absorbs ultra-violet rays from the sun, preventing them from reaching the Earth's surface. This is the primary and most critical function of the ozone layer, protecting life on Earth from harmful solar radiation.
The question asks about the general distribution of water vapour in the atmosphere with respect to altitude. To answer this, we need to recall the atmospheric processes related to water, such as evaporation, condensation, and the role of temperature.
Correct Option: B) Decreases with increasing altitude
This is correct because the main source of water vapour is the Earth's surface, and as air rises, it cools, leading to condensation and a reduced capacity to hold moisture. Therefore, the concentration of water vapour is highest near the surface and decreases significantly with increasing altitude.
The question asks about the approximate percentage of water vapour in the air by volume in warm and wet tropical regions. This requires knowledge of atmospheric composition, specifically the variable components like water vapour.
Correct Option: D) 4 per cent. In warm and wet tropical regions, the air is nearly saturated with moisture. Water vapour can constitute up to approximately 4% of the air by volume in such conditions. This is the upper limit for water vapour concentration in the atmosphere.
The question asks about the proportion of water vapour in the air in dry and cold regions like deserts and polar areas. This requires knowledge of atmospheric composition and how environmental factors affect water vapour content.
Correct Option: C) Less than one per cent of the air. In dry and cold regions like deserts and polar areas, the atmospheric conditions (lack of moisture sources in deserts, extremely low temperatures in polar regions) severely limit the amount of water vapour the air can hold. Consequently, water vapour constitutes a very small fraction of the air, typically less than one per cent.