Answer
See explanation.
Work Step by Step
(a) The work done by the gas in isothermal process is
$W = nRTln (\frac{V_2}{V_1})$
$W = (0.15) (8.314 J/mol.K) (350K ) (ln (\frac{0.25V_1}{V_1})$
$W = -605 J$
(b) $\Delta U = nC_V \Delta T $
In isothermal process, the temperature is constant, hence, $\Delta T = 0$
$\Delta U = nC_V (0)$
$\Delta U = 0 $
(c) $\Delta U = Q - W$
$0 = Q - W$
$Q = W$ when $W = -605 J$
$Q = -605 J$
The gas released heat to the surrounding as indicated by the negative sign.
