b
Potential of point $\mathrm{N}=20 \mathrm{\,V}$
Potential difference will be shared in inverse ratio of capacitances.
$\mathrm{V}_{\mathrm{N}}-\mathrm{V}_{\mathrm{A}}=10 \mathrm{\,V}$
$\mathrm{V}_{\mathrm{B}}-\mathrm{V}_{\mathrm{N}}=\frac{10}{3}, \quad \mathrm{V}_{\mathrm{B}}-\mathrm{V}_{\mathrm{N}}=\frac{2 \times 10}{3}$
$\therefore \mathrm{V}_{\mathrm{B}}=\frac{20}{3}+\mathrm{V}_{\mathrm{A}}=\frac{20}{3}+10=\frac{50}{3}$
