JEE Main · 2026 · 28 Jan 2026 · Shift 1 · p-Block Elements

Down group 15 the E\textendash H bond becomes longer and weaker, so the thermal stability of the hydrides falls in the order $\mathrm{NH}{}_3>\mathrm{PH}{}_3>\mathrm{AsH}{}_3>\mathrm{SbH}{}_3$. As the hydrides grow less stable they give up hydrogen more readily, so their reducing power rises down the group. The lone pair on E occupies an increasingly large, diffuse orbital, so it becomes less available for donation and the basicity falls from $\mathrm{NH}{}_3$ to $\mathrm{SbH}{}_3$. Boiling point, however, does not climb steadily: strong intermolecular hydrogen bonding lifts $\mathrm{NH}{}_3$ far above $\mathrm{PH}{}_3$, giving the irregular order $\mathrm{PH}{}_3<\mathrm{AsH}{}_3<\mathrm{NH}{}_3<\mathrm{SbH}{}_3$. The correct statements are that stability decreases, basicity decreases and reducing character increases down the group.