Which of the following statements is NOT correct regarding the catalytic ability of transition metals?

decrease the concentration of reactant at catalyst surface

The correct answer is Option (2) → decrease the concentration of reactant at catalyst surface

Let's analyze the statements about transition metals as catalysts:

1. Ability to exist in variable oxidation states 
• True; allows them to participate in redox cycles and catalyze reactions.
2. Decrease the concentration of reactant at catalyst surface 
• Incorrect. Catalysts adsorb reactants, often increasing their effective concentration at the surface, not decreasing it.
3. Activation energy is lowered 
• True; catalysts provide an alternative pathway with lower activation energy.
4. Weakens the bond in the reacting molecules 
• True; adsorption on the metal surface often weakens bonds, facilitating reaction.