In which of the processes does the internal energy of the system remain constant?

$A$ poly-atomic molecule $(C_v = 3R, C_p = 4R$,where $R$ is the gas constant) goes from phase space point $A (P_A = 10^5 \ Pa, V_A = 4 \times 10^{-6} \ m^3)$ to point $B (P_B = 5 \times 10^4 \ Pa, V_B = 6 \times 10^{-6} \ m^3)$ and then to point $C (P_C = 10^4 \ Pa, V_C = 8 \times 10^{-6} \ m^3)$. The path $A$ to $B$ is adiabatic and the path $B$ to $C$ is isothermal. The net heat absorbed per unit mole by the system is:

An ideal gas expands isothermally along $ab$ and does $600\,J$ of work. During the process,

Two ideal gases $A$ and $B$ of the same number of moles expand at constant temperatures $T_1$ and $T_2$ respectively such that the pressure of gas $A$ decreases by $50 \%$ and the pressure of gas $B$ decreases by $75 \%$. If the work done by both the gases is same, then $T_1: T_2$ is:

If an ideal gas is compressed isothermally,then:

Work done by a system under isothermal change from a volume $V_1$ to $V_2$ for a gas which obeys Van der Waals' equation $(V - n\beta) \left( P + \frac{\alpha n^2}{V^2} \right) = nRT$.