For which of the following processes, entropy change is zero?

$1$ mole of gas with $\gamma =\frac{7}{5}$ is mixed with $1$ mole of gas with $\gamma =\frac{5}{3}$, then the value of $\gamma$ for the resulting mixture is

An ideal gas is taken through the cycle $A\to B\to C\to A$, as shown in the figure below. If the net heat supplied to the gas is $5\mathrm{J}$, then the work done by the gas in the process $C\to A$ is