The average distance of an electron in an atom from its nucleus is of the order of:

Which of the following statements is correct about the cathode rays?
$1$. These rays start from anode and move towards cathode.
$2$. They are visible with human eye.
$3$. In presence of electric and magnetic fields,they behave like positively charged particles.
$4$. Their characteristic does not depend on the nature of material at electrode.

The relationship between the radius of the nucleus $(R)$ and the mass number $(A)$ is given by .......

Who discovered the proton and the neutron?

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

Rutherford's $\alpha$-particle scattering experiment is related to the size of the ..........