Among electron, proton, neutron and $\alpha $ - particle, the maximum penetration capacity is for:
A. electron
B. proton
C. neutron
$\text{D}\text{. }\!\!\alpha\!\!\text{ -particle}$

Hint: Penetration capacity is the ability of a substance to penetrate inside a material. More the penetration capacity, more will the given particle or wave will penetrate into a given material.

Complete step by step answer:
Penetration capacity is the ability of a substance to penetrate inside a material. More the penetration capacity, more will the given particle or wave will penetrate into a given material. This property is shown by a wave. We know that every particle has a wave nature. The wavelength of particles or bodies of large masses is very large. Therefore, we cannot see the wave nature of these bodies with our naked eyes. Particles like electrons have very small mass hence they have very small wavelengths.
The penetration power or capacity of a particle depends on the energy and mass of the particle. Higher the energy greater is the penetration power. Larger the mass, less is the penetration power of the particle. Charge on the particle also affects its penetration power. The charge on the particle should be less for greater penetration capacity.
Among the given particles, $\text{ }\!\!\alpha\!\!\text{ -particle}$ , which is a helium ion, has the largest mass. Therefore, it has the least penetrating power. Electrons , protons and neutrons have higher energy than $\text{ }\!\!\alpha\!\!\text{ -particle}$. Electron and proton have charge of e whereas neutron is neutral in charge, the penetration capacity of neutron is the highest.
Therefore, the correct option is C.

Note: Penetration power also depends on the ionizing energy of the particle. Penetration power of a particle is inversely proportional to the ionizing energy of the particle. Therefore, a particle having low ionizing energy will have a high penetration power.