c
Current in each branch $=\frac{10}{4}=2.5 \mathrm{\,A}$
$\mathrm{V}_{\mathrm{C}}-\mathrm{V}_{\mathrm{A}}=2.5 \times 1$ ..........$(i)$
$\mathrm{V}_{\mathrm{C}}-\mathrm{V}_{\mathrm{B}}=2.5 \times 3$ ............$(ii)$
eq. $(ii)$ $-$ $(i)$
$V_{A}-V_{B}=2.5(3-1)=5 \mathrm{\,V}$