Are neutrons present in all atomic nuclei? Explain.

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 ......... .

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.

Neutrons are found in atoms of all elements except in

The nature of anode rays depends upon:

Radius of the nucleus is equal to $10^{-12} \ cm$ and that of the atom is equal to $10^{-8} \ cm$. What is the fraction of the volume of the atom occupied by the nucleus?