Correct option is : (4) \( C_{V}+\frac{R}{2 V}\)
\(\mathrm{dQ}=\mathrm{du}+\mathrm{dW}\)
\(\mathrm{CdT}=\mathrm{C}_{\mathrm{V}} \mathrm{dT}+\mathrm{PdV}\) ...........(1)
\(\therefore\ \ \mathrm{PV}^{2}=\mathrm{RT}\)
\(\mathrm{P}=\) constant
\(\mathrm{P}(2 \mathrm{VdV})=\mathrm{RdT}\)
\(\mathrm{PdV}=\frac{\mathrm{RdT}}{2 \mathrm{V}}\)
Put in equation (1)
\( \mathrm{C}=\mathrm{C}_{\mathrm{V}}+\frac{\mathrm{R}}{2 \mathrm{V}} \)