Read the passage carefully and answer the questions.
The transition metals and their compounds are known for their catalytic activity. This activity is ascribed to their ability to adopt multiple oxidation states and to form complexes. Vanadium(V) oxide (in Contact Process), finely divided iron, and nickel (in Catalytic Hydrogenation) are some of the examples. Catalysts at a solid surface involve the formation of bonds between reactant molecules and atoms of the surface of the catalyst (first row transition metals utilise 3d and 4s electrons for bonding). This has the effect of increasing the concentration of the reactants at the catalyst surface and also weakening of the bonds in the reacting molecules (the activation energy is lowering). Also because the transition metal ions can change their oxidation states, they become more effective as catalysts.
Which of the following is incorrect about the ability of catalytic action of transition metals?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → weakening of the bonds in the reacting molecules-catalyst complex
Transition metals are good catalysts because they can adopt multiple oxidation states and can form complexes. On a solid catalyst the reactant molecules bond to the atoms of the surface; this raises their concentration there and weakens the bonds inside the reacting molecules, so the activation energy is lowered.
Option (1) ability to form complexes — A correct statement about the catalytic action. The reactants are held on the metal as short-lived complexes, which react and then leave the metal free again.
Option (2) ability to adopt multiple oxidation states — A correct statement about the catalytic action. A metal ion that can change its oxidation state can take electrons from one reactant and pass them on to another; \( \ce{Fe^3+} \) in the iodide–persulphate reaction is the standard example.
Option (3) weakening of the bonds in the reacting molecules-catalyst complex — Not a correct statement about the catalytic action. What is weakened is the set of bonds within each reacting molecule. The bonds between the reactant and the catalyst surface are newly formed; they hold the reactant on the surface. Option (3) puts the weakening on the “reacting molecules–catalyst complex” instead of on the bonds of the reacting molecules themselves.
Option (4) formation of bonds between reactant molecules and catalyst — A correct statement about the catalytic action. This bonding at the surface is the first step of heterogeneous catalysis.
NCERT (2026-27 edition):
Catalytic Properties
