Environmental Science MCQ – Asked in Previous Years, WBCS Mains

Answer – B. Chlorofluorocarbon
Explanation-Chlorofluorocarbons (CFCs) are primarily responsible for the depletion of the ozone (O3) layer. CFCs were widely used in various industrial applications, such as aerosol propellants, refrigerants, and foam-blowing agents. When released into the atmosphere, CFCs rise to the stratosphere, where they undergo photodissociation by UV radiation. This process releases chlorine atoms that catalytically destroy ozone molecules, leading to the thinning of the ozone layer.

Answer – D. CO (carbon monoxide)
Explanation-Carbon monoxide (CO) is a gas that reacts with hemoglobin in red blood cells, forming carboxyhemoglobin. This reduces the ability of hemoglobin to carry oxygen, leading to a decrease in the oxygen-carrying capacity of the blood. Carbon monoxide poisoning can have severe health effects and can be fatal in high concentrations. It is produced by the incomplete combustion of carbon-based fuels such as gasoline, natural gas, and coal.

Answer – B. Methane (CH4)
Explanation-Methane (CH4) is the main constituent of both biogas and natural gas. Biogas is produced through the anaerobic digestion of organic materials, such as agricultural waste, sewage, and food waste. Natural gas, on the other hand, is primarily formed by the decomposition of organic matter over millions of years deep within the Earth’s crust. Methane is a potent greenhouse gas and a valuable source of energy when captured and utilized.

Answer – C. Oil slicks in the sea increase dissolved oxygen content.
Explanation-
Oil slicks in the sea do not increase dissolved oxygen content. In fact, oil spills can have detrimental effects on marine ecosystems, including the depletion of dissolved oxygen. Oil forms a layer on the water surface, preventing the exchange of gases between the atmosphere and the water. Microorganisms that break down organic matter in the water column consume oxygen, leading to oxygen depletion and the formation of “dead zones” where marine life cannot survive.

Answer – A. Si (Silicon)
Explanation-
Silicon (Si) is the major element present in Earth’s crust. It is the second most abundant element after oxygen and constitutes approximately 27.7% of the Earth’s crust by weight. Silicon is widely distributed in various minerals, including quartz, feldspar, mica, and clay. It is a key component of rocks, soils, and minerals, playing a significant role in the structure and composition of the Earth’s crust.

Answer – A. Recharge groundwater
Explanation-The aim of rainwater harvesting is to recharge groundwater. Rainwater harvesting is the process of collecting and storing rainwater for future use. It involves the capture and storage of rainwater runoff from rooftops, land surfaces, and other areas. One of the primary objectives of rainwater harvesting is to replenish or recharge groundwater aquifers. By directing rainwater into the ground, it helps to maintain or increase groundwater levels, which is essential for sustainable water supply.

Answer – C. Terrestrial
Explanation-Grasslands are included in the terrestrial ecosystem. Terrestrial ecosystems encompass all land-based ecosystems, including forests, grasslands, deserts, tundra, and more. Grasslands are characterized by vast stretches of land covered primarily by grasses and herbaceous plants. They can be found in different climatic regions worldwide and support a variety of plant and animal species adapted to grassland environments.

Answer – D. Plantation and Forestation
Explanation-Plantation and forestation assist in environmental protection. Planting trees and establishing forests play a crucial role in preserving and protecting the environment. Trees and forests help in mitigating climate change by absorbing carbon dioxide, providing habitat for wildlife, preventing soil erosion, improving air and water quality, and supporting biodiversity. Plantation and forestation efforts contribute to the conservation and sustainable management of natural resources.

Answer – A. Air
Explanation-The largest reservoir of nitrogen gas (N2) in the environment is the air, specifically the Earth’s atmosphere. Nitrogen gas makes up approximately 78% of the Earth’s atmosphere. Although nitrogen is abundant in the atmosphere, it is relatively inert and not readily available for use by most organisms. Nitrogen fixation, carried out by certain bacteria and lightning, converts atmospheric nitrogen into forms that can be utilized by plants and other living organisms.

Answer – A. Acid rain
Explanation-Soil is rarely contaminated due to acid rain. Acid rain is a form of precipitation that contains high levels of sulfuric acid and nitric acid, which are formed when emissions from industrial processes and vehicles react with atmospheric moisture. Acid rain can have harmful effects on the environment, including soil and water bodies. When acid rain falls on the ground, it can lower the pH of the soil, making it more acidic. This increased acidity can have adverse effects on soil organisms, beneficial microorganisms, and soil structure. It can also leach essential nutrients from the soil, making them less available for plants and affecting their growth.