Environmental Science MCQ – Asked in Previous Years, WBCS Mains

Answer – A. Cyanobacteria
Explanation-Water blooms, also known as algal blooms, are mostly caused by cyanobacteria. Cyanobacteria, also called blue-green algae, are a group of photosynthetic bacteria that can rapidly multiply and form dense colonies in water bodies under favorable conditions. These blooms often occur in nutrient-rich waters and can lead to the discoloration of water, depletion of oxygen, and the release of harmful toxins, posing risks to aquatic organisms and ecosystems.

Answer – B. Gulf of Mexico
Explanation-The largest oil spill recorded so far occurred in the Gulf of Mexico. It was the result of the Deepwater Horizon oil rig explosion in April 2010. The incident led to a massive release of oil from the wellhead, causing extensive environmental damage to marine ecosystems, coastlines, and wildlife in the Gulf of Mexico region. The spill highlighted the risks and consequences associated with offshore oil drilling.

Answer – D. 7 – 7.9
Explanation-

Answer – D. Uttarakhand forest fire
Explanation-Among the given options, the Uttarakhand forest fire is considered a natural disaster. Forest fires can occur naturally due to various factors, such as lightning strikes or spontaneous combustion. They can cause significant damage to forests, wildlife habitats, and human settlements, posing risks to biodiversity, air quality, and human lives. The Bhopal Gas tragedy, Chernobyl accident, and Exxon Valdez oil spill, on the other hand, were industrial accidents or incidents caused by human activities rather than natural disasters.

Answer – B. sentinel species
Explanation-Sentinel species are organisms that are particularly sensitive to changes in their environment. They act as indicators or early warning signs of environmental changes, including pollution, habitat degradation, or the presence of toxins. Sentinel species are often monitored to assess the health of ecosystems and the potential risks to other organisms, including humans. Their sensitivity to environmental changes makes them valuable in environmental monitoring and conservation efforts. Keystone species, on the other hand, are species that have a disproportionately large impact on their ecosystem’s structure and function. Endangered species and vulnerable species are classifications based on their risk of extinction.

Answer – C. DO (Dissolved Oxygen)
Explanation-Air pollution refers to the contamination of the air by pollutants that can have harmful effects on human health, the environment, and ecosystems. The term “SMOG” refers to a type of air pollution characterized by a mixture of smoke and fog. “MMD” is not a commonly used abbreviation in the context of air pollution and does not correspond to a specific term. “DO” (Dissolved Oxygen) is a term used in the context of water quality to measure the amount of oxygen dissolved in water, not air pollution. “VC” is not commonly used in the context of air pollution and does not correspond to a specific term.

Answer – B. Noise pollution
Explanation- Mufflers are devices used in vehicle exhaust systems to reduce the noise generated by the engine. They are designed to attenuate or dampen the sound waves produced during the combustion process, thus reducing the noise pollution caused by vehicles. Mufflers are not used to prevent radiation pollution, air pollution, or thermal pollution.

Answer – C. 135 dB
Explanation-Prolonged exposure to high levels of noise can lead to various physiological disorders. The threshold for pain from sound is generally considered to be around 120-130 decibels (dB). Continuous exposure to noise levels exceeding 85 dB can cause hearing damage, and at higher levels, around 135 dB, it can cause immediate physiological effects such as pain, hearing impairment, and other health issues.

Answer – C. Hydrogen
Explanation-PAN formation does not include hydrogen. PAN is a secondary pollutant, which means it is not emitted directly into the atmosphere, but is formed from other pollutants by chemical reactions. PAN is formed when nitrogen oxides (NOx) and volatile organic compounds (VOCs) react in the presence of sunlight.

The chemical reaction that forms PAN is as follows:
NO₂ + RO₂ + hv → PAN + O₂

Answer – A. 1
Explanation-The global warming potential (GWP) is a measure of the greenhouse effect caused by a particular substance compared to the effect of carbon dioxide (CO2), which is assigned a GWP of 1. CO2 is considered the baseline reference for calculating the impact of other greenhouse gases. Other greenhouse gases, such as methane (CH4) and nitrous oxide (N2O), have higher GWPs compared to CO2, indicating that they have a greater warming effect over a specific time period. Note: The specific time period (e.g., 20 years, 100 years) for which the GWP is calculated may vary, but the GWP of CO2 is generally defined as 1 over a 100-year time horizon.