The $1^{\text {st }}, 2^{\text {nd }}$ and the $3^{\text {rd }}$ ionization enthalpies $\mathrm{I}_1, \mathrm{I}_2$ and $\mathrm{I}_3$, of four atoms with atomic numbers $\mathrm{n}, \mathrm{n}+1$, $n+2$ and $n+3$, where $n<10$, are tabulated below. What is the value of $n$ ?
