Which of the following is TRUE of a catalyst? I. it alters the activation energy of a reaction II. it is…

Analyzing the question: We must decide which of the four statements about a catalyst are true.

Concept: A catalyst is a substance that changes the rate of a chemical reaction by providing an alternative pathway with a different activation energy. It is not used up, and it does not change the position of equilibrium or the overall energy change of the reaction.

Checking each statement:

• I. It alters the activation energy of a reaction. TRUE. A catalyst provides an alternative route with a lower activation energy (a negative catalyst or inhibitor raises it, so "alters" is correct).
• II. It is effective in a reaction but cannot initiate a reaction. TRUE, in the standard textbook sense. A catalyst speeds up a reaction that is already thermodynamically possible. It cannot make a non-spontaneous reaction happen.
• III. It affects the equilibrium of a reversible reaction. FALSE. A catalyst speeds up the forward and reverse reactions equally, so equilibrium is reached faster but the equilibrium position and the equilibrium constant do not change.
• IV. It affects the overall reaction. FALSE. The catalyst is regenerated at the end. It does not change the overall stoichiometry, the products, or the enthalpy change (ΔH).

Result: Only I and II are true.

Answer: A. I and II only

Exam tip: Remember "catalysts change the speed, not the destination." They change the rate and the activation energy, but never the equilibrium position, ΔH, or the yield at equilibrium. Any option claiming a catalyst affects equilibrium can be eliminated immediately.