Explanation

(d) Specific heat for a monoatomic gas
$C_{V} = \frac{3}{2}R$
$\therefore\ \ \ Heat\ \ \ \ d\mathcal{Q =}\mu C_{V}\mathrm{\Delta}T$
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ d\mathcal{Q\ =}\mu \times \frac{3}{2} \times R(473 - 273)$
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ = 4 \times \frac{3}{2} \times R \times 200\ \ \ \ (\because\mu = 4)$
$\therefore$ $d\mathcal{Q} = 4 \times 300R$
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ = 1200R$