Statement: Solid catalyst does not affect equilibrium conversion (Option C)

Explanation:

Introduction:
In a gas-phase reversible reaction, reactant molecules adsorb onto the surface of a solid catalyst, react, and then desorb as product molecules. The catalyst plays a crucial role in enhancing the rate of the reaction by providing an active site for adsorption and promoting the reaction. However, the equilibrium conversion of a reversible reaction is determined solely by the thermodynamics of the reaction and is unaffected by the presence of a solid catalyst.

Equilibrium Conversion:
Equilibrium conversion is the ratio of the concentration of the reactant at equilibrium to the initial concentration of the reactant. It is a measure of how far the reaction proceeds in the forward direction at equilibrium. The equilibrium conversion is determined by the equilibrium constant (K) of the reaction, which is a function of temperature and the stoichiometry of the reaction.

Effect of a Solid Catalyst on Equilibrium Conversion:
1. Adsorption is not rate-limiting (Option A):
- Adsorption of reactant molecules onto the catalyst surface is typically a fast process and is not the rate-limiting step in the reaction.
- The rate of adsorption is determined by the concentration of reactant molecules and the availability of active sites on the catalyst surface.
- Therefore, the rate of adsorption does not affect the equilibrium conversion.

2. Desorption is not rate-limiting (Option B):
- Desorption of product molecules from the catalyst surface is also typically a fast process and is not the rate-limiting step in the reaction.
- The rate of desorption is determined by the concentration of product molecules and the availability of active sites on the catalyst surface.
- Therefore, the rate of desorption does not affect the equilibrium conversion.

3. Temperature affects equilibrium conversion (Option D):
- According to Le Chatelier's principle, an increase in temperature favors the endothermic reaction and decreases the equilibrium conversion, while a decrease in temperature favors the exothermic reaction and increases the equilibrium conversion.
- Therefore, temperature does affect the equilibrium conversion.

Conclusion:
The statement "Solid catalyst does not affect equilibrium conversion" (Option C) is always true. The equilibrium conversion of a gas-phase reversible reaction is solely determined by the thermodynamics of the reaction and is unaffected by the presence of a solid catalyst.