b
\(\sin \theta=\frac{10}{20}=\frac{1}{2}\)

\(\theta=30^{\circ}\)

\(\tan \theta=\frac{\mathrm{qE}}{\mathrm{mg}}\)

\(\tan 30^{\circ}=\frac{\mathrm{q} \times 2 \times 10^4}{1 \times 10^{-3} \times 10}\)

\(\frac{1}{\sqrt{3}}=\mathrm{q} \times 10^6\)

\(\mathrm{q}=\frac{1}{\sqrt{3}} \times 10^{-6} \mathrm{C}\)

\(x=3\)