(b)
$\frac{e}{m}for\ electron\ (e) = \frac{1.6 \times 10^{- 19}}{9.1 \times 10^{- 28}}$
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ = 1.758 \times 10^{8}$
$\frac{e}{m}for\ proton\ (p) = \frac{1.6 \times 10^{- 19}}{1.672 \times 10^{- 24}}$
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ = 9.56 \times 10^{4}$
$\frac{e}{m}for\ neutron\ (n) = \frac{0}{1.675 \times 10^{- 24}} = 0$
$\frac{e}{m}for\ \alpha - particle = \frac{2}{4} = 0.5$
Hence, the increasing order of $\frac{e}{m}$ is as
$n < \alpha < p < e$