Given below are two statements: One is labelled as Assertion $(A)$ and the other is labelled as Reason $(R)$
Assertion $(A)$: Enthalpy of neutralisation of strong monobasic acid with strong monoacidic base is always $-57 \ kJ \ mol^{-1}$.
Reason $(R)$: Enthalpy of neutralisation is the amount of heat liberated when one mole of $H^{+}$ ions furnished by acid combine with one mole of $OH^{-}$ ions furnished by base to form one mole of water.
In the light of the above statements,choose the correct answer from the options given below.

• A
  $(A)$ is true but $(R)$ is false.
• B
  Both $(A)$ and $(R)$ are true and $(R)$ is the correct explanation of $(A)$.
• C
  $(A)$ is false but $(R)$ is true.
• D
  Both $(A)$ and $(R)$ are true but $(R)$ is not the correct explanation of $(A)$.