JEE Main 2023 · 10 April · evening · 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 : Physical properties of isotopes of hydrogen are different.
Reason R : Mass difference between isotopes of hydrogen is very large.
In the light of the above statements, choose the correct answer from the options given below:
- (a) A is true but R is false
- (b) Both A and R are true but R is NOT the correct explanation of A
- (c) A is false but R is true
- (d) Both A and R are true and R is the correct explanation of A
Answer and solution
Answer (d) Both A and R are true and R is the correct explanation of A
Solution
Chemistry ma’am · 4 steps
Deuterium is twice as heavy as protium, so its physical properties change, and that mass gap is the reason.
- Three isotopes. Hydrogen has three isotopes: protium, deuterium and tritium. All three have one proton and one electron. They differ only in the number of neutrons.
Isotope Neutrons Mass number Mass compared to protium Protium, ¹₁H 0 1 1 times Deuterium, ²₁H or D 1 2 2 times Tritium, ³₁H or T 2 3 3 times - Check R. One extra neutron doubles the mass of the hydrogen atom. No other element has isotopes whose masses differ by such a large fraction. So R is true.
- Check A. Chemical properties depend on electrons, so they are almost the same. Physical properties such as melting point, boiling point, density and rate of diffusion depend on mass. For example, D₂ boils a few kelvin higher than H₂. So A is true.
- So. The physical properties differ because the relative mass difference is so large, so R is the correct explanation of A. The answer is (d).
The idea to keep. Isotopes share electrons, so their chemistry matches. Physical properties follow mass, and for hydrogen the relative mass gap (1 : 2 : 3) is the largest of any element.
Answer from the NTA final answer key. Solution by PrepWiser.