The increase order for the value of $e/m$ (charge to mass ratio) for electron $\left(e\right)$, proton $\left(p\right)$; neutron $\left(n\right)$ and alpha particle $\left(\alpha \right)$ is:

The correct option is B $n<\alpha <p<e$

The e/m ratio is known as specific charge where, $e$ is the charge on particle and $m$ is mass of the particles.

For neutrons $\Rightarrow$ charge is zero.

mass $=1.6\times {10}^{-27}$ amu

For proton $\Rightarrow$ charge $=1.6\times {10}^{-19}C$

mass $=1.6\times {10}^{-27}$ amu

For electron $\Rightarrow$ charge $=1.6\times {10}^{-19}C$

mass $=9.1\times {10}^{-31}$ amu

For $\alpha -$particle $\Rightarrow$ charge $\Rightarrow 2\times 1.6\times {10}^{-19}C$

mass $\Rightarrow 4\times 1.6\times {10}^{-27}$ amu

From these data, it can be concluded that neutron has least (e/m) specific charge and electron has high e/m ratio.

$n<\alpha <p<e$