How did Chadwick discover the neutron? Explain.

Which particle leaves no track in a Wilson cloud chamber?

The radius of a nucleus with mass number $A$ is given by $1.25 \times 10^{-13} \times A^{1/3} \ cm$. If the radius of the atom is $1 \ \mathring{A}$ and the mass number is $64$,calculate the fraction of the volume occupied by the nucleus.

Proton was discovered by

Which of the following statements regarding cathode rays is incorrect?

Fill in the blanks:
$(i)$ For the discovery of neutrons,$\alpha$-particles were bombarded on a thin sheet of ......... .
$(ii)$ For the $\alpha$-particle scattering experiment,Rutherford used a gold foil of thickness ......... .
$(iii)$ The radius of an atom is approximately ......... and the radius of the nucleus is ......... .
$(iv)$ The entire positive charge of an atom is concentrated in a very small region,which is called ......... .