Question

The density of KBr is 2.75 g cm-³; the length of the unit cell is 654 pm. K = 39, Br = 80. What is true about the predicted nature of the solid?

A. Solid has face-centered cubic system with coordination number = 6
B. Solid has simple cubic system with coordination number = 4
C. Solid has face-centered cubic system with coordination number = 1
D. None of these

Answer 1

Considering the properties of KBr provided, it is clear that KBr crystallizes in a face-centered cubic lattice, which would typically have a coordination number of 12. So, the correct option is D. 'None of these'.

Step-by-step explanation:

The student asked about the predicted nature of the solid KBr with a given density and unit cell length. Potassium bromide (KBr) crystallizes in a face-centered cubic (FCC) lattice. Considering the provided density (2.75 g/cm³) and the length of the unit cell (654 pm), we can deduce the nature of the KBr solid.

In an FCC lattice, each unit cell has four formula units of the compound. The coordination number in an FCC structure is 12, meaning each ion is surrounded by 12 opposite ions. Given the values for atomic weights of K (39) and Br (80) and the provided density, we can calculate the number of formula units per unit cell. However, since the coordination number provided in the options does not match the FCC structure, the correct answer would be 'None of these'.