JEE Main 2020 · 8 January · evening · Single correct · +4 / −1
For the following Assertion and Reason, the correct option is
Assertion : For hydrogenation reactions, the catalytic activity increases from Group 5 to Group 11 metals with maximum activity shown by Group 7-9 elements.
Reason : The reactants are most strongly adsorbed on group 7-9 elements.
- (a) Both assertion and reason are true and the reason is the correct explanation for the assertion.
- (b) The assertion is true, but the reason is false.
- (c) Both assertion and reason are true but the reason is not the correct explanation for the assertion.
- (d) Both assertion and reason are false.
Answer and solution
Answer (b) The assertion is true, but the reason is false.
Solution
Chemistry ma’am · 4 steps
The assertion is the textbook trend, but the reason fails: the best catalyst adsorbs moderately.
- Check the assertion. For hydrogenation, the catalytic activity of metals increases from Group 5 to Group 11, and the peak activity is shown by Group 7 to 9 elements. This is a standard NCERT statement, so the assertion is true.
- How activity works. A catalyst works through chemisorption. The reactants must be held strongly enough to loosen their bonds, but weakly enough that they can still move, react and let the product leave the surface.
- Check the reason. If adsorption is too strong, the reactants and products stay stuck to the surface and block it, so activity falls. Group 7 to 9 metals are the best because their adsorption strength is moderate, not the strongest. The reason is false.
- So. The assertion is true and the reason is false, which is option (b).
The idea to keep. Good catalysts follow a middle path: adsorption strong enough to activate reactants, weak enough to let products leave. Strongest adsorption means a poisoned, slow surface.
Answer from the NTA final answer key. Solution by PrepWiser.