When an electron hits a $\mathrm{ZnS}$ screen, scintillation is produced.

The nature of anode rays depends upon the nature of residual gas.

The energy of an electron is negative.

The radius of the nucleus is of the order of ${10}^{-12} \mathrm{cm}$. 

The radius of an atom is of the order of ${10}^{-8} \mathrm{cm}$.

The nature of cathode rays depends upon the nature of gas taken in the discharge tube.

Isotopes of an element differ in their masses.