In salt AB, B forms simple cubic lattice and A particles are present at the body centre of each unit cell. If one of the B goes missing from every unit cell, the molecular formula of the salt will become-
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → \(A_8B_7\)
In a unit cell, a corner particle is shared by 8 unit cells, so it counts 1/8; a body-centre particle belongs wholly to one cell.
\( \displaystyle \text{B at 8 corners: } 8 \times \frac{1}{8} = 1 \)
\( \displaystyle \text{A at the body centre: } 1 \)
So the perfect salt is AB. If one B is missing from every unit cell, only 7 corners stay occupied:
\( \displaystyle \text{B} = 7 \times \frac{1}{8} = \frac{7}{8}, \qquad \text{A} = 1 \)
\( \displaystyle \text{A : B} = 1 : \frac{7}{8} = 8 : 7 \)
The formula becomes A8B7.
Note: 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.