(Ist law of thermodynamics) $\Rightarrow \Delta \mathrm{Q}=\Delta \mathrm{u}+\mathrm{P} \Delta \mathrm{v}$
or $150=\Delta u+100(1-2)$
$=\Delta u-100$
$\therefore \Delta u=150+100=250 \mathrm{J}$
Thus the internal energy of the gas increases by $250 \mathrm{J}$
Reason $R$ : The efficiency of Carnot's engine depends not only on temperature of cold reservoir but it depends on the temperature of hot reservoir too and is given as $\eta=\left(1-\frac{ T _2}{ T _1}\right)$.
In the light of the above statements, choose the correct answer from the options given below


