$\mathrm{W}=\mathrm{n} \mathrm{RT} \log _{\mathrm{e}} \frac{\mathrm{V}_{2}}{\mathrm{V}_{1}}$
For, $n=1$
$\mathrm{W}=\mathrm{RT} \ln \frac{\mathrm{V}_{2}}{\mathrm{V}_{1}}$
For an isothermal process, $\Delta \mathrm{U}=0$ $\Delta \mathrm{Q}=\Delta \mathrm{U}+\mathrm{W}=0+\mathrm{RT} \ln \frac{\mathrm{V}_{2}}{\mathrm{V}_{1}}$
$\therefore$ Entropy $=\frac{\Delta Q}{T}=R \ln \frac{V_{2}}{V_{1}}$
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($1$) Which of the following options is the only correct representation of a process in which $\Delta U=\Delta Q-P \Delta V$ ?
$[A] (II) (iv) (R)$ $[B] (II) (iii) (P)$ $[C] (II) (iii) (S)$ $[D] (III) (iii) (P)$
($2$) Which one of the following options is the correct combination?
$[A] (III) (ii) (S)$ $[B] (II) (iv) (R)$ $[C] (II) (iv) (P)$ $[D] (IV) (ii) (S)$
($3$) Which one of the following options correctly represents a thermodynamic process that is used as a correction in the determination of the speed of sound in an ideal gas?
$[A] (III) (iv) (R)$ $[B] (I) (ii)$ $(\mathrm{Q})$ $[C] (IV) (ii) (R)$ $[D] (I) (iv) (Q)$
Statement $-I$ : What $\mu$ amount of an ideal gas undergoes adiabatic change from state $\left( P _{1}, V _{1}, T _{1}\right)$ to state $\left( P _{2}, V _{2}, T _{2}\right)$, the work done is $W =\frac{1 R \left( T _{2}- T _{1}\right)}{1-\gamma}$, where $\gamma=\frac{ C _{ P }}{ C _{ V }}$ and $R =$ universal gas constant,
Statement $-II$ : In the above case. when work is done on the gas. the temperature of the gas would rise.
Choose the correct answer from the options given below

