|The increasing order (lowest to highest) of e/m (charge/mass) ratio is $$ n < \alpha < p < e$$.|
Neutron being neutral has zero charges and lowest e/m ratio. An electron has a unit charge but negligible mass. Hence, the electron has a maximum e/m ratio.
For an alpha particle, the e/m ratio is 2/4 or 0.5.
For proton, e/m ratio is 1/1 or 1.