Then increasing order for the value of e/m for the electron, proton, neutron and $\alpha$ particle is:

The correct option is D $n,\alpha ,p,e$
Since the neutron has no charge, it's e/m value is zero.

$\alpha$ particle has very high mass occupied to the electron as well as proton there will be a very small e/m ratio.

Proton and electron have the same charge ($q=1.6\times {10}^{-19}C$ ) but the former is just heavier, therefore it has a smaller value of e/m.

Mass of proton, $m_p=1.67\times {10}^{-27}Kg$

Mass of electron, $m_e=9.1\times {10}^{-31}Kg$

$\because m_p>m_e$

$\therefore {\left(e/m\right)}_e>{\left(e/m\right)}_p$

So, the correct order is $n,\alpha ,p,e$

Hence, the correct option is D.