The nuclides of $^{197}_{79} \text{Au}$ and $^{198}_{80} \text{Hg}$ are called . . . . . . of each other.

The ratio of the density of oxygen nucleus $\left({ }_{8}^{16} O \right)$ and helium nucleus $\left({ }_{2}^{4} He \right)$ is (in $:1$)

Consider the following statements:
$I$. All isotopes of an element have the same number of neutrons.
$II$. Only one isotope of an element can be stable and non-radioactive.
$III$. All elements have isotopes.
$IV$. All isotopes of carbon can form chemical compounds with oxygen-$16$.
Choose the correct option regarding an isotope.

Match the following types of nuclei with their respective examples:

Column-$I$	Column-$II$
$A$. Isotopes	$i$. $Li^7, Be^7$
$B$. Isobars	$ii$. $_8O^{18}, _9F^{19}$
$C$. Isotones	$iii$. $_1H^1, _1H^2$

What is the particle $x$ in the following nuclear reaction :
${ }_4^9 Be+{ }_2^4 He \rightarrow{ }_6^{12} C+x$

In the following nuclear reaction $_{12}Mg^{24} + _{2}He^{4} \to _{14}Si^{X} + _{0}n^{1}$,the value of $X$ is: