d
As valtage dropacioss $8\, \Omega=\sqrt{2 \times 8}=4 \mathrm{\,V}\left(\because P=\frac{\mathrm{V}^{2}}{\mathrm{R}}\right)$
Therefore voltage drop across $3\, \Omega=3 \mathrm{\,V}$
$[\because 4 \mathrm{\,V} $is divided in ratio of resistances between $1\, \Omega $ and $ 3 \,\Omega$]
Hence power dissipated in $3 \Omega=\frac{(3)^{2}}{3}=3$ $\mathrm{watt}$