Under ordinary aqueous acid–base conditions, which of the following statements…

Concept

For group-15 hydrides, basicity depends on how readily the central atom’s lone pair can accept a proton. Acid–base classification must also be tied to the stated medium: reactions requiring a nonaqueous superbase do not define ordinary aqueous behavior.

Application

1. In NH3, nitrogen is treated as sp3-hybridized, and its lone pair is available to bind H+, forming NH4+.

2. In PH3, the P–H bonds use orbitals with little hybridization, while the lone pair has high 3s character and is held more tightly. Removal of a P–H proton requires exceptionally strong nonaqueous bases, outside the stated conditions.

3. Therefore PH3 accepts a proton less readily than NH3 and is the weaker base (less alkaline substance).

Cross-check

The conjugate acid NH4+ is far more stable in water than PH4+, which is consistent with NH3 being the stronger base. Hence the true statement is: PH3 is less alkaline than NH3.

Contrast

• “PH3 is more alkaline than NH3” reverses the effect of lone-pair availability.

• Under ordinary aqueous conditions, “PH3 is amphoteric” assigns a proton-donor pathway that is not available in the stated medium.

• “More than one of the above” does not apply because only the less-alkaline comparison is supported.

• “None of the above” does not apply because the less-alkaline comparison is supported.