Achange in which factor will affect the rate of reaction only when gases are involved?
temperature
pressure
surface area
concentration

Pressure affects the rate of reaction when only gases are involved.

Explanation: For writing the rate of reaction, we use law of mass action, which is:

This is the case when all the reactants and products are in solid or liquid states.

But in the case of gases, we replace concentration in the above equation by the partial pressures of reactants and products, so the rate equation becomes:

So, the factor that effects the rate of reaction when only gases are involved is Pressure.