(A): Introduction of catalyst does not affect position of equilibrium

(R): For a reversible reaction, presence of a catalyst influences both forward & backward reaction to the same extent

 When a catalyst is present, the equilibrium is achieved faster but its magnitude remains unaffected. Thus, the value of the equilibrium constant in presence of a catalyst is same as in the absence of a catalyst. This is because the catalyst influences the rate of forward reaction and reverse reaction to same extent. Hence the correct answer is (A) Both $A\&R$ are true, $R$ is the correct explanation of $\mathrm{A}$.