Which of the following processes is reversible?

What is an irreversible process and what is a reversible process?

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 thermodynamic process is quasi-static and does not dissipate energy?

Two cylinders $A$ and $B$ of equal capacity are connected to each other via a stop cock. Cylinder $A$ contains an ideal gas at standard temperature and pressure. Cylinder $B$ is completely evacuated. The entire system is thermally insulated. The stop cock is suddenly opened. The process is:

Which process is acceptable in nature: a reversible or an irreversible process?