JEE Main · 2025 · 28 Jan 2025 · Shift 2 · p-Block Elements

Nitrogen, the lightest group 15 element, has no accessible d-orbitals and so cannot form $d\pi -d\pi$ bonds with transition metals. Phosphorus, arsenic, antimony and bismuth all have available d-orbitals and can form such bonds. Basicity of the group 15 hydrides falls steadily down the group as the lone pair becomes more diffuse and less available for donation, so among the hydrides capable of $d\pi -d\pi$ bonding ($P{H}_3$, $As{H}_3$, $Sb{H}_3$, $Bi{H}_3$), $P{H}_3$ is the strongest base. The element is phosphorus, atomic number 15.