Write the relation of the size of the nucleus to the atomic size. 

The particles which can be added to the nucleus of an atom without changing its chemical properties are called

$STATEMENT-1$: The plot of atomic number ( $\mathrm{y}$-axis) versus number of neutrons ( $\mathrm{x}$-axis) for stable nuclei shows a curvature towards $x$-axis from the line of $45^{\circ}$ slope as the atomic number is increased. and  $STATEMENT-2$: Proton-proton electrostatic repulsions begin to overcome attractive forces involving protons and neutrons and neutrons in heavier nuclides.

The mass number of a nucleus is

The nuclear force between two nucleons is explained by

Given below are two statements: one is labelled as Assertion $A$ and the other is labelled as Reason $R$

Assertion $A:$ The binding energy per nucleon is practically independent of the atomic number for nuclei of mass number in the range $30$ to $170$.

Reason $R$ : Nuclear force is short ranged.

In the light of the above statements, choose the correct answer from the options given below on