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.

We start by reading the assertion carefully. It states that during catalytic hydrogenation the activity of transition-metal catalysts increases steadily from the metals of Group 5 to the metals of Group 11, and that the highest activity is observed for the centre of this block, namely the metals of Groups 7, 8 and 9. Experimental data from industrial hydrogenation processes (for example, the high activity of $$\text{Fe},\ \text{Co},\ \text{Ni}$$ compared to $$\text{V}$$ or $$\text{Cu}$$) fully support this statement. Therefore, the assertion is true.

Now we examine the reason. The reason claims that “the reactants are most strongly adsorbed on Group 7-9 elements.” In heterogeneous catalysis we recall the fundamental principle known as Sabatier’s principle: a good catalyst must adsorb reactant molecules neither too weakly nor too strongly; instead, an intermediate strength of adsorption is required so that the reactants are activated on the surface but the products can still desorb. If adsorption is too strong, the surface becomes poisoned because the products or reactants refuse to leave; catalytic turnover then falls.

Hence, what actually gives Group 7-9 metals their maximum catalytic activity is that they provide this optimum, moderate adsorption energy, not the strongest adsorption energy. The wording “most strongly adsorbed” contradicts Sabatier’s principle and the observed behaviour of early transition metals (Groups 4-6) that indeed adsorb too strongly and therefore show lower hydrogenation activity. Consequently, the reason is false.

We therefore have:

$$\text{Assertion: True}, \quad \text{Reason: False}$$

So the combination that matches is “The assertion is true, but the reason is false,” which corresponds to Option A.

Hence, the correct answer is Option A.