115 practice questions covering Nature's Treasures, organised into 1 topics.
115 questions include a written explanation.
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A news report says that the oil wells of a certain country may run dry in about forty years. This is possible because petroleum is
Aa non-renewable resource present in a limited amount
Bformed afresh in the ground every rainy season
Ca renewable resource that returns with every monsoon
Dmade in refineries out of ordinary air
Show answer and explanation
Correct answer: A - a non-renewable resource present in a limited amount
An oil field holds a fixed store of petroleum that took millions of years to form, so steady pumping can empty it. Rain has nothing to do with refilling it. A refinery only separates petroleum that has already been pumped up; it cannot make oil from air, and no fresh oil forms each season.
Q2
easy
Soil is formed mainly from
Aplastic waste that breaks down within a week
Brocks that slowly break into tiny pieces over a very long time
Cair that settles down on the ground
Dwater that freezes into ice during winter
Show answer and explanation
Correct answer: B - rocks that slowly break into tiny pieces over a very long time
Wind, water and changes of temperature break rock into smaller and smaller pieces over hundreds of years, and these pieces mix with the remains of plants and animals to make soil. Ice, air and plastic waste do not build soil. Plastic stays in the ground for years without breaking down at all.
Q3
hard
Consider these statements. (i) A row of trees planted along the edge of a field slows the wind and protects the soil. (ii) Leaving land completely bare through the dry season makes its soil richer. Which of them is correct?
AOnly (ii)
BBoth (i) and (ii)
COnly (i)
DNeither (i) nor (ii)
Show answer and explanation
Correct answer: C - Only (i)
Statement (i) is correct, because a line of trees breaks the force of the wind and stops it from carrying away dry topsoil. Statement (ii) is wrong, since bare land loses soil to wind and rain and gains no humus. Hence only the first statement is correct.
Q4
medium
Consider these statements. (i) Oxygen is the most plentiful gas in air. (ii) Carbon dioxide forms only a very small part of air. Which of them is correct?
ABoth (i) and (ii)
BOnly (ii)
CNeither (i) nor (ii)
DOnly (i)
Show answer and explanation
Correct answer: B - Only (ii)
Statement (ii) is correct, as carbon dioxide is a tiny fraction of air even though plants need it to make food. Statement (i) is wrong because nitrogen, not oxygen, is the most plentiful gas in air. Choosing (i) or choosing both repeats that mistake, and rejecting both throws away a true statement.
Q5
easy
Which gas makes up the largest part of the air around us?
ANitrogen
BCarbon dioxide
COxygen
DWater vapour
Show answer and explanation
Correct answer: A - Nitrogen
Nitrogen is about $78\%$ of air by volume, far more than any other gas. Oxygen comes next at about $21\%$, so it is not the largest part. Carbon dioxide is a very tiny share of air even though plants depend on it. Water vapour changes from place to place and is always a small share.
Q6
medium
The dark upper layer of soil is rich in humus. Humus is made of
Afine sand carried in by the wind
Bsalt left behind by rainwater
Csmall chips of hard, unbroken rock
Dthe rotted remains of plants and animals
Show answer and explanation
Correct answer: D - the rotted remains of plants and animals
Humus is the dark, crumbly material formed when dead leaves, roots and animal remains rot in the soil, and it makes the topsoil fertile. Rock chips, salt and blown sand may all be present in soil, but none of them is humus, and none of them supplies the nutrients that humus does.
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