Question

Given below are two statements. Assertion (A): Kerosene oil is put on stagnant water to prevent the spread of malaria. Reason (R): Kerosene is poisonous to mosquitoes. Choose the most appropriate answer.

• A. Both (A) and (R) are correct and (R) is the correct explanation of (A)
• B. Both (A) and (R) are correct but (R) is not the correct explanation of (A)
• C. (A) is correct but (R) is not correct
• D. (A) is not correct but (R) is correct

Hint:

Stagnant water supports mosquito breeding; kerosene forms a surface layer and kills or suffocates mosquito larvae.

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
The question asks us to evaluate whether pouring kerosene on still water is an effective method for controlling malaria and if the underlying mechanism is due to the chemical toxicity of kerosene to mosquitoes.

Step 2: Detailed Explanation:
Let us analyze the biological and physical mechanisms:
• Assertion (A): Sprinkling kerosene on the surface of stagnant water is indeed used to prevent the breeding of mosquitoes, helping in malaria treatment and prevention. This statement is correct.

• Reason (R): Kerosene is described here as being "poisonous" to mosquitoes. However, kerosene does not kill mosquito larvae through chemical poisoning or toxicity. Instead, it works mechanically:

• Pouring kerosene forms a thin layer on the water's surface, which reduces the surface tension.

• This thin film blocks the breathing tubes (siphons) of the mosquito larvae hanging at the water surface, cutting off their oxygen supply and suffocating them.
Thus, the primary eradication mechanism is suffocation, not toxicity. Therefore, the reason is scientifically incorrect.

Step 3: Final Answer:
Assertion (A) is correct, but Reason (R) is incorrect. This corresponds to option (C).