$\mathrm{R}_{2}=\mathrm{R}+\mathrm{S}=1 \,\Omega+2 \,\Omega=3 \,\Omega$

$\mathrm{I}_{1} \mathrm{R}_{1}=\mathrm{I}_{2} \mathrm{R}_{2}$

$\mathrm{I}_{1}=\frac{\mathrm{R}_{2}}{\mathrm{R}_{1}} \mathrm{I}_{2}=\frac{3}{6} \mathrm{I}_{2}=\frac{\mathrm{I}_{2}}{2}$

or $\mathrm{I}_{2}=2 \mathrm{I}_{1}$

Heat flow $\mathrm{H}=\mathrm{I}^{2} \mathrm{Rt}$

For $Q, H_{Q}=I_{1}^{2} Q t=\frac{I_{2}^{2}}{4} \times 4 t=I_{2}^{2} t$

For $\mathrm{S}, \mathrm{H}_{\mathrm{S}}=\mathrm{I}_{2}^{2} \mathrm{St}=\mathrm{I}_{2}^{2} \cdot 2 \mathrm{t}=2 \mathrm{I}_{2}^{2} \mathrm{t}$

$\therefore $ Greatest amount of heat generated by $S$.