(A): The enthalpy of neutralization of a strong acid by a strong base is a constant.

(R): The net reaction that takes place is the same.

Enthalpy of neutralization: - It is the enthalpy charge that takes place when 1g equivalent of an acid (or base) in neutralized by $1\mathrm{ }\mathrm{g}$-equivalent of a base (or acid) in dilute solution.

The enthalpy of neutralization of any strong acid and strong base is always constant, i.e. $57.1\mathrm{ }\mathrm{k}\mathrm{J}$ because both the acid and base undergo complete ionization.

Hence the correct answer is (A) Both $\mathrm{A}$ and $\mathrm{R}$ are true and $\mathrm{R}$ is the correct explanation.