JEE Main 2023 · 6 April · morning · Single correct · +4 / −1
Given below are two statements, one is labelled as Assertion A and the other is labelled as Reason R.
Assertion A : Loss of electron from hydrogen atom results in nucleus of ∼ 1.5 × 10⁻³ pm size.
Reason R : Proton (H⁺) always exists in combined form.
In the light of the above statements, choose the most appropriate answer from the options given below:
- (a) Both A and R are correct and R is the correct explanation of A
- (b) A is correct but R is not correct
- (c) A is not correct but R is correct
- (d) Both A and R are correct but R is NOT the correct explanation of A
Answer and solution
Answer (d) Both A and R are correct but R is NOT the correct explanation of A
Solution
Chemistry ma’am · 4 steps
The tiny size of H⁺ is the cause and its combined existence is the result, so R cannot explain A.
- Check Assertion A. A hydrogen atom has only one electron. Remove it and only the bare proton is left, of size about 1.5 × 10⁻³ pm. Ordinary atoms and ions are about 50 to 200 pm across, so A is correct.
- Check Reason R. A bare proton is extremely small, so its charge density is enormous. It attaches at once to any molecule nearby, for example H⁺ + H₂O → H₃O⁺. So H⁺ never exists free, and R is correct.
- Test the link. Ask: does R tell us why the nucleus is so small? No. The size follows from the atom losing its only electron. R is a consequence of A. It is not the reason behind A.
- So. Both statements are true, but R does not explain A. The answer is (d).
The idea to keep. In assertion-reason questions, ask which statement causes the other. If R follows from A, then R cannot be the explanation of A, even when both are true.
Answer from the NTA final answer key. Solution by PrepWiser.