Assertion: Ammonia gas is lighter than air.
Reason: The molecular weight of ammonia is less than that of air.
Both assertion and reason are true, and the reason is the correct explanation of the assertion.
Both assertion and reason are true, but the reason is not the correct explanation of the assertion.
The assertion is true, but the reason is false.
The assertion is false, but the reason is true.
Correct Option A
The Assertion is true. Ammonia gas is lighter than air because it has a lower molecular weight than air. The molecular weight of ammonia is 17 g/mol, while the average molecular weight of air is 29 g/mol.
The Reason is also true and provides the correct explanation for the Assertion. The molecular weight of a gas determines its density relative to air. A gas with a lower molecular weight than air will be less dense and therefore lighter than air. Since ammonia has a lower molecular weight than air, it is less dense and lighter than air. Hence option A is the correct answer.
Option (B) is incorrect because it incorrectly states that the assertion is correct but the reason is incorrect. Both the assertion and reason are correct. Hence option B is incorrect.
Option (C) is incorrect because it incorrectly states that the assertion is incorrect but the reason is correct. The assertion is correct, and the reason is also correct. Hence option C is incorrect.
Option (D) is incorrect because it incorrectly states that both the assertion and reason are incorrect. Both the assertion and reason are correct. Hence option D is incorrect.