(b) Given, $v = 2.18\ \times 10^{6}\ {ms}^{- 1},\ r = 0.528\ \times \ 10^{- 10}m$
Acceleration of electron moving round the nucleus
$\ \ \ \ \ \ \ \ \ \ \ \ \ a\ =$ $\frac{\left( 2.18\ \times 10^{6} \right)^{2}}{0.528\ \times 10^{- 10}} \approx$ $9\ \times 10^{22}\ ms^{- 2}$