b
(b) For monoatomic gas
$\gamma = \frac{{{C_P}}}{{{C_V}}} = \frac{5}{3}$
we know $\Delta Q = n{C_P}\Delta T$ and $\Delta U = n{C_V}\Delta T$
==> $\frac{{\Delta U}}{{\Delta Q}} = \frac{{{C_V}}}{{{C_P}}} = \frac{3}{5}$
i.e. fraction of heat energy to increase the internal energy be $3/5.$