The mass of an atom is constituted mainly by

The nucleus and an atom can be assumed to be spherical. The radius of the nucleus of mass number $A$ is given by $R_n = 1.25 \times 10^{-13} \times A^{1/3} \, \text{cm}$. The atomic radius is $1 \, \mathring{A}$. If the mass number is $64$,the fraction of the atomic volume that is occupied by the nucleus is:

Which one of the following pairs is not correctly matched?

The number of electrons in the nucleus of $^{12}C$ is

Who discovered the ratio of charge to mass of an electron and how? Explain with a diagram.

The $\alpha$-particle is identical with