In the following reaction $_{12}M{g^{24}}{ + _2}H{e^4}{ \to _{14}}S{i^X}{ + _0}{n^1},X$ is

$(a)$ Two stable isotopes of lithium $_{3}^{6} L$ and $_{3}^{7} L$ have respective abundances of $7.5 \%$ and $92.5 \% .$ These isotopes have masses $6.01512\; u$ and $7.01600\; u ,$ respectively. Find the atomic mass of lithium.

$(b)$ Boron has two stable isotopes, $_{5}^{10} B$ and $^{11}_{5} B$. Their respective masses are $10.01294 \;u$ and $11.00931\; u$, and the atomic mass of boron is $10.811\; u$. Find the abundances of $_{5}^{10} B$ and $_{5}^{11} B$

$STATEMENT-1$: 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.

Atomic weight of boron is $10.81$ and it has two isotopes $_5{B^{10}}$ and $_5{B^{11}}$. Then ratio of  $ _5{B^{10}}{\,:\,_5}{B^{11}} $ in nature would be

Nuclear forces are