There is no change in internal energy of an ideal gas when it undergoes

$A$ process can be reversible if

$Assertion :$ Reversible systems are difficult to find in the real world.
$Reason :$ Most processes are dissipative in nature.

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 :

Which of the following is an irreversible process?

$A$ thermally insulated container is divided into two parts by a screen. In one part,an ideal gas is filled at pressure $P$ and temperature $T$. The second part is a vacuum. If a small hole is now created in the screen,the temperature of the gas will: