JEE Main · 2023 · 29 Jan 2023 · Shift 2 · Classification of Elements and Periodicity

The first ionization enthalpies are $B=801$, $Al=577$ and $Ga=579\mathrm{kJ}\mathrm{mo}{\mathrm{l}}^{-1}$. From B to Al the value falls by about $224\mathrm{kJ}\mathrm{mo}{\mathrm{l}}^{-1}$ (large decrease, from the big rise in atomic size), whereas from Al to Ga it does not fall at all $-$ Ga is in fact marginally higher. So the decrease from B to Al is much larger than that from Al to Ga, and Statement I is correct. Gallium is $[\mathrm{Ar}]3d^{10}4s^{2}4p^1$: its 3d orbitals are completely filled, and these $3d^{10}$ electrons shield the 4p electron poorly, raising the effective nuclear charge and explaining why IE does not drop from Al to Ga. Statement II is also correct. Hence both statements are correct.