A

Step 1: Consider the initial and final states of the system. Initially, the left half contains gas at temperature T0, while the right half is a vacuum (evacuated).
Step 2: When the hole is opened, the gas begins to expand into the evacuated half. This is a free expansion process, which is an irreversible process.
Step 3: Since the chamber is insulated, there is no heat exchange with the walls (Q = 0). As the gas undergoes free expansion, no work is done on or by the system (W = 0) because it expands into a vacuum.
Step 4: According to the first law of thermodynamics, \Delta U = Q - W. Since Q = 0 and W = 0, we have \Delta U = 0. This means the internal energy remains constant.
Step 5: For an ideal gas, the internal energy is a function of temperature. Thus, if the internal energy is constant, the temperature must also remain constant.
Therefore, the final temperature of the system, after reaching equilibrium, remains T0.