JEE Main · 2024 · 30 Jan 2024 · Shift 2 · p-Block Elements

Down group 15, the M–H bond weakens as the central atom grows larger, so thermal stability of the hydrides falls: ${\text{NH}}_3>{\text{PH}}_3>{\text{AsH}}_3>{\text{SbH}}_3>{\text{BiH}}_3$ — Statement A is correct. A weaker M–H bond releases hydrogen more readily, so reducing power rises down the group in the same order, ${\text{NH}}_3<{\text{PH}}_3<{\text{AsH}}_3<{\text{SbH}}_3<{\text{BiH}}_3$ — Statement B is correct. This makes ${\text{NH}}_3$ the weakest reducing agent and ${\text{BiH}}_3$ the strongest, the reverse of Statement C, which is false. Basicity depends on how available the lone pair is for donation; down the group the lone pair sits in a larger, more diffuse orbital and is held less tightly to a smaller extent of s-character, so basicity actually decreases down the group, ${\text{NH}}_3>{\text{PH}}_3>{\text{AsH}}_3>{\text{SbH}}_3>{\text{BiH}}_3$ — Statement D, which claims the opposite order, is false. Statements A and B are correct.