Given below are two statements. One is labelled as Assertion $(A)$ and the other is labelled as Reason $(R)$.
Assertion $(A) :$ In an insulated container,a gas is adiabatically shrunk to half of its initial volume. The temperature of the gas decreases.
Reason $(R) :$ Free expansion of an ideal gas is an irreversible and an adiabatic process.
In the light of the above statement,choose the correct answer from the options given below :

• A
  Both $(A)$ and $(R)$ are true and $(R)$ is the correct explanation of $(A)$
• B
  $(A)$ is true but $(R)$ is false
• C
  $(A)$ is false but $(R)$ is true
• D
  Both $(A)$ and $(R)$ are true but $(R)$ is $\text{NOT}$ the correct explanation of $(A)$