Ans: (B)
Hint \(: \sigma \frac{4}{3} \pi r^{3} g=6 \pi \eta r v, v=\frac{2}{9} \frac{\sigma r^{2} g}{\eta}, v=\frac{2}{9} \times \frac{10^{3} \times 0.9 \times 10^{-3} \times 0.9 \times 10^{-3} \times 9.8}{1.8 \times 10^{-5}}, v=98 \mathrm{~m} / \mathrm{s}\)