Question

In a solid ‘AB’ having the NaCl structure, ‘A’ atoms occupy the corners of the cubic unit cell. If all the facecentred atoms along one of the axes are removed, then the resultant stoichiometry of the solid is

(A) AB₂ 

 (B) A₂ B 

(C) A₄ B₃ 

(D) A₃ B₄

Answer 1

Correct option (D) A₃ B₄

Explanation:

In NaCl, Na+ occupies body centre and edge centres while Cl– occupies corners and face centres, giving four Na⁺ and four Cl^– per unit cell. In the present case, A represent Cl^– and B represents Na⁺. Two face centres lies on one axis.

⇒ Number of A removed = 2 x 1/2 = 1

Number of B is removed because it is not present on face centres.

⇒ A remaining = 4 – 1 = 3 

B remaining = 4 

⇒ Formula = A₃ B₄