The rate of reaction is equal to the specific rate constant, when:

Explanation

When the concentration of all the reactants collectively is unity, the rate of reaction is equal to the specific rate constant. This is because in the rate equation:Rate = k [A]^m [B]^nwhere [A] and [B] are the concentrations of the reactants, and m and n are the reaction orders.If the collective concentration of the reactants is unity, meaning [A] * [B] = 1, then the rate equation simplifies to:Rate = kThis shows that when the concentration of the reactants collectively is unity, the rate of reaction is equal to the specific rate constant (k).Therefore, the correct answer is a) Concentration of reactants collectively is unity.