The thermodynamic process,in which the internal energy of the system remains constant is ...........

For the $P-V$ diagram given for an ideal gas,which of the following correctly represents the $T-P$ diagram?

$A$ gas is compressed at constant temperature. Its molecules gain:

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 $(V - n\beta) \left( P + \frac{\alpha n^2}{V^2} \right) = nRT$.

$Assertion :$ The isothermal curves intersect each other at a certain point.
$Reason :$ The isothermal change takes place slowly,so,the isothermal curves have very little slope.

During an isothermal expansion,a confined ideal gas does $-150 \, J$ of work against its surroundings. This implies that