Q70. Which farming practice rotates different crops to maintain soil fertility and interrupt pest cycles?
[WBCS Mains – Environmental Science (2022)]
(A) Monoculture
(B) Biological control alone
(C) Crop sharing
(D) Crop rotation
Answer: (D) Crop rotation
Explanation: Crop rotation alternates crops over seasons and may include legumes that add nitrogen. The change disrupts pest life cycles and helps manage soil nutrients, potentially lowering fertiliser and pesticide requirements.
Q69. A food chain based on dead organic matter and decomposer organisms is a:
[WBCS Mains – Environmental Science (2022)]
(A) Parasitic food chain
(B) Detritus food chain
(C) Grazing consumer chain
(D) Predator-only chain
Answer: (B) Detritus food chain
Explanation: Detritus food chains begin with dead plant and animal matter. Fungi, bacteria and detritivores break it down, enabling nutrient recycling and transferring energy to organisms that consume the decomposers.
Q68. Which soil pH range is generally suitable for cultivating many common crops?
[WBCS Mains – Environmental Science (2022)]
(A) 3.4–5.4
(B) 6.5–7.5
(C) 4.5–8.5
(D) 5.5–6.5
Answer: (B) 6.5–7.5
Explanation: Many crop plants grow best near neutral soil pH because major nutrients remain accessible and root activity is efficient. Individual crops vary, however, and some acid-loving plants need substantially lower pH.
Q67. Which bulky solid by-product is characteristic of the iron and steel industry?
[WBCS Mains – Environmental Science (2022)]
(A) Red mud
(B) Fly ash
(C) Bottom ash
(D) Granulated slag
Answer: (D) Granulated slag
Explanation: Blast-furnace and steel-making processes generate slag from fluxes and impurities. Granulated slag can be processed into cementitious materials, while red mud is associated mainly with alumina refining.
Q66. DDT is classified in conventional pollution questions as:
[WBCS Mains – Environmental Science (2022)]
(A) Not a pollutant
(B) An antibiotic
(C) A persistent non-biodegradable pollutant
(D) A readily biodegradable pollutant
Answer: (C) A persistent non-biodegradable pollutant
Explanation: DDT is a persistent organochlorine pesticide that degrades slowly and can accumulate in food webs. Its environmental persistence and effects on wildlife drove restrictions under international chemical agreements.
Q65. Which factor would directly counter the oxygen shortage in an already eutrophic water body?
[WBCS Mains – Environmental Science (2022)]
(A) Increase dissolved oxygen
(B) Increase nutrient inputs
(C) Increase algal blooms
(D) Increase decomposition bacteria
Answer: (A) Increase dissolved oxygen
Explanation: Aeration can immediately raise dissolved oxygen and relieve hypoxia in an existing eutrophic water body. For durable prevention, reducing nitrogen and phosphorus inputs is also essential because aeration alone does not remove the underlying excess nutrients.
Q64. A pyramid of numbers at a trophic level records the number of:
[WBCS Mains – Environmental Science (2022)]
(A) Species in a region
(B) Individuals in the whole community
(C) Organisms at that trophic level
(D) Subspecies in the region
Answer: (C) Organisms at that trophic level
Explanation: A pyramid of numbers describes counts of individual organisms at each feeding level. Its shape depends on ecosystem type and can invert when one large tree supports numerous herbivorous insects.
Q63. Which of these is not an in-situ conservation site for wild plants?
[WBCS Mains – Environmental Science (2022)]
(A) Biosphere reserve
(B) Botanical garden
(C) National park
(D) Wildlife sanctuary
Answer: (B) Botanical garden
Explanation: Botanical gardens cultivate plants outside their original habitats and are therefore examples of ex-situ conservation. National parks, sanctuaries and biosphere reserves primarily protect organisms in natural or near-natural locations.
Q62. Which Indian region is a recognised global biodiversity hotspot?
[WBCS Mains – Environmental Science (2022)]
(A) Western Ghats
(B) Nanda Devi alone
(C) Eastern Ghats as a separate hotspot
(D) Aravalli Range
Answer: (A) Western Ghats
Explanation: The Western Ghats form part of the Western Ghats–Sri Lanka biodiversity hotspot, noted for high endemism and threats to natural habitat. A hotspot is identified by both exceptional plant endemism and major habitat loss.
Q61. Photochemical smog characteristically contains which component?
[UPPSC PCS Prelims – GS Paper I (2022)]
(A) Phosphorus
(B) Ozone
(C) Methane
(D) Aluminium ions
Answer: (B) Ozone
Explanation: Sunlight-driven reactions between nitrogen oxides and volatile organic compounds create ground-level ozone, a defining component of photochemical smog. Its presence is linked to respiratory symptoms and reduced agricultural yields.
