The atomic mass number of an element is $\qquad$ .

The ratio of the radii of nuclei $_{13}Al^{27}$ and $_{52}X^A$ is $3:5$. The number of neutrons in the nucleus of $X$ will be:

$A$ nucleus has mass number $A_1$ and volume $V_1$. Another nucleus has mass number $A_2$ and volume $V_2$. If the relation between the mass numbers is $A_2 = 3 A_1$,then $\frac{V_1}{V_2} =$

Consider the following statements ($X$ and $Y$ stand for two different elements):
$(I)$ ${ }_{32}^{65} X$ and ${ }_{33}^{65} Y$ are isotopes.
$(II)$ ${ }_{42}^{86} X$ and ${ }_{42}^{85} Y$ are isotopes.
$(III)$ ${ }_{85}^{174} X$ and ${ }_{88}^{177} Y$ have the same number of neutrons.
$(IV)$ ${ }_{92}^{235} X$ and ${ }_{94}^{235} Y$ are isobars.
Which of the above statements are correct?

The charge density $P$ in a nucleus varies with distance $r$ from the centre of the nucleus according to the curve in the figure. Which of the following graphs correctly represents this variation?

Find the ratio of the radii of the nuclei $_{13}Al^{27}$ and $_{52}Te^{125}$.