ChemistryInorganic: P Block Elements

Generally, Group 15 elements in -3 oxidation state form binary compou…

Generally, Group 15 elements in \(-3\) oxidation state form binary compounds with metals of type \(M_3X_2\) (X = N, P, As, Sb, Bi). Which of the following elements may not have an ore with formula \(M_3X_2\)?

(A) N

(B) P

(D) Sb

(E) Bi

Choose the correct answer from the options given below:

Answer & explanation

Correct answer: option 2

The correct answer is Option (2) → (C) only

All Group 15 elements react with metals to form binary compounds in the −3 oxidation state. For a divalent metal (M²⁺) the charges balance as M₃X₂: 3(+2) + 2(−3) = 0. The examples are:

    (A) N: \( \ce{Ca3N2} \) (calcium nitride) — M₃X₂
    (B) P: \( \ce{Ca3P2} \) (calcium phosphide) — M₃X₂
    (C) As: the example is sodium arsenide. Sodium is monovalent, so the charges balance as 3(+1) + (−3) = 0, i.e. Na₃As (see Note 1), a compound of the type M₃X, not M₃X₂
    (D) Sb: \( \ce{Zn3Sb2} \) (zinc antimonide) — M₃X₂
    (E) Bi: \( \ce{Mg3Bi2} \) (magnesium bismuthide) — M₃X₂

Note 1: The pre-rationalised NCERT book prints Na₃As₂; it should read Na₃As (three Na⁺ ions balance one As³⁻ ion).

Note 2: This question is from the pre-rationalised NCERT book (2022-23). The topic is not there in the latest NCERT book (2026-27), and it is also out of the CUET 2026 syllabus.

NCERT (Pre-rationalised edition, 2022-23):
Reactivity towards Metals

Textbook extract