Question

Assertion (A): DDT (an insecticide) has now become almost ineffective against mosquitoes.

Reason (R): Introduction of DDT brought a change in the gene frequency with a shift from DDT-sensitive to DDT-resistant mosquitoes.

Options

• Both assertion (A) and reason (R) are true, and reason is the correct explanation of assertion.

• Both assertion (A) and reason (R) are true, but reason is not the correct explanation of assertion.

• Assertion (A) is true but reason (R) is false.

• Both assertion (A) and reason (R) are false.

Answer 1

Both assertion (A) and reason (R) are true, and reason is the correct explanation of assertion.

Explanation:

DDT kills susceptible mosquitoes while resistant individuals survive and reproduce. Over generations, the resistant type becomes more common and DDT becomes less effective.