Explanation

(c) $\mathrm{\Delta}Q = \mu C_{P}\mathrm{\Delta}T = \frac{7}{2}\mu R\mathrm{\Delta}T\ \ \left\lbrack C_{P} = \frac{7}{2}R \right\rbrack$
$\mathrm{\Delta}U = \mu C_{V}\mathrm{\Delta}T = \frac{5}{2}\mu R\mathrm{\Delta}T\ \ \left\lbrack C_{V} = \frac{5}{2}R \right\rbrack$
and $\mathrm{\Delta}W = \mathrm{\Delta}Q - \mathrm{\Delta}U = \mu R\mathrm{\Delta}T$
$\Rightarrow \ \mathrm{\Delta}Q:\mathrm{\Delta}U:\mathrm{\Delta}W = 7:5:2$