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33 questions with worked solutions.
Q1. Which of these are particulates?
Answer: All of these
Particulates are small solid or liquid particles suspended in air. Dust, fumes, fly ash, smoke, and mist all fit this broad category, so every option listed contains particulates.
Q2. Untreated domestic sewage has a low:
Answer: BOD value
Untreated domestic sewage contains a large amount of biodegradable organic matter, so microorganisms consume more oxygen while breaking it down. That means its BOD is high, not low; the dissolved oxygen percentage is the one that tends to be low.
Q3. Which is among the greatest contributors to gaseous pollutions that are responsible for acidic rain?
Answer: Electrical power generation using coal
Coal-fired power plants emit sulfur dioxide and nitrogen oxides, which react in the atmosphere to form acids that fall as acid rain. The other choices are not major direct contributors in the same way.
Q4. Chlorofluorocarbons (CFCs) are widely used in air conditioners, refrigerators etc, because of being:
Answer: non-reactive
CFCs are used in cooling systems because they are chemically inert under normal conditions, so they do not readily react with the components of the appliance or the refrigerant cycle. Their non-reactivity makes them suitable for long-term use in sealed systems.
Q5. Which of the following is a nonbiodegradable pollutant?
Answer: DDT
DDT is a synthetic pesticide that is highly persistent and does not decompose easily, so it is considered nonbiodegradable. Sewage, plant leaves, and domestic wastes are generally biodegradable because microorganisms can break them down.
Q6. Sulphur dioxide levels in the atmosphere can be reduced by using:
Answer: Low-sulphur fuels
Sulphur dioxide is produced when sulfur in fuel burns, so using fuel with less sulfur directly reduces the amount formed. The other options may help with other pollutants, but they do not specifically cut SO2 as effectively.
Answer: Green chemistry
This is green chemistry because it aims to design chemical processes that reduce or eliminate the use of hazardous substances. Replacing toxic hexavalent chromium with trivalent chromium makes the plating process safer and more environmentally friendly.
Q8. Hydrocarbon PCB is called \( a s \)
Answer: polychlorinated biphenyls
PCB stands for polychlorinated biphenyls. The term refers to biphenyl compounds with multiple chlorine atoms substituted on the aromatic rings.
Q9. Plastic used to preserve yogurts is replaced with a polymer called polylactic acid is an example of
Answer: green chemistry
Replacing conventional plastic with polylactic acid is an example of designing a more environmentally friendly material. That fits green chemistry because it focuses on creating safer, renewable, and less polluting chemical products and processes.
Q10. Which of the following is not a major greenhouse gas?
Answer: calcium carbonate
Carbon dioxide, methane, and water vapour are all important greenhouse gases because they absorb and re-emit infrared radiation. Calcium carbonate is a solid compound found in rocks and shells, not a greenhouse gas.
Q11. Assertion Plastics are non-biodegradable. Reason As they cannot be decomposed by micro-organisms.
Answer: Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
Plastics are generally non-biodegradable because most common plastics are not decomposed by micro-organisms. So the reason directly explains why the assertion is true.
Q12. Aerosols, decrease primary productivity by
Answer: Reducing photosynthesis
Aerosols can scatter and absorb incoming solar radiation, reducing the light available for photosynthesis. With less photosynthesis, plants and phytoplankton make less organic matter, so primary productivity decreases.
Q13. Monuments of marble can be destroyed by:
Answer: sulphur dioxide pollution
Sulphur dioxide dissolves in water to form acidic compounds, leading to acid rain. Acid reacts with marble (calcium carbonate), causing it to erode and lose detail over time.
Q14. Which of the following is not properly matched?
Answer: Photochemical smog - Green air
Photochemical smog is associated with brownish haze, not green air. The other pairs are standard matches: formaldehyde is carcinogenic, sulphur dioxide causes respiratory irritation, and nitrogen oxides contribute to brown air.
Answer: Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
Carbon monoxide is poisonous because it binds strongly with haemoglobin to form carboxyhaemoglobin. This reduces haemoglobin’s ability to carry oxygen, causing oxygen deprivation in tissues.
Q16. The amount of oxygen required to oxidise organic substances present in water is called:
Answer: Biochemical oxygen demand (BOD)
Biochemical oxygen demand (BOD) is the amount of dissolved oxygen needed by microorganisms to decompose organic substances in water. It reflects the biodegradable organic pollution load, unlike DO which is the oxygen already available in water.
Q17. Which of the following is a sink for CO?
Answer: Microorganism present in the soil
Microorganisms in the soil can metabolize carbon monoxide (CO) and act as a natural sink, reducing its concentration in the atmosphere.
Q18. Which one of the following statements is not true?
Answer: When the pH of rain water is higher than 6.5, it is called acid rain.
Acid rain occurs when the pH of rainwater is below 5.6, not above 6.5. Hence, statement D is incorrect.
Q19. Which one of the following statement is not true?
Answer: Concentration of DO below 6 ppm is good for the growth of fish.
The statement 'Concentration of DO below 6 ppm is good for the growth of fish' is incorrect because dissolved oxygen (DO) levels below 6 ppm are generally harmful to aquatic life, including fish.
Q20. Green chemistry means such reactions which:
Answer: reduce the use and production of hazardous chemicals
Green chemistry focuses on designing chemical processes and products that minimize the use and generation of hazardous substances, promoting environmental sustainability.