If the radious of `Cs^(o+) = 1.69 Å` and `Br^(Θ) = 1.95 Å`, then which of the following is//are correct statement?

Options

A. The edge length of unit cell is `4.2 Å`.
B. The coordination number for `Cs^(o+)` is `6`.
C. `CsBr` has bcc-type structure.
D. `Br^(Θ)` ions touch each other along the edge.

Answer

A, C

Explanation

`(r_(Cs^(o+)))/(r_(Be^(ɵ))) = 1.69/1.95 = 0.867` (bcc structure)
Hence, `Cs^(o+)` ion lies at the "body centre of cubic void where" `CN` of `Cs^(o+) = 8`.
`CsBr` has bcc sturucture with `Br^(ɵ)` froming simple cubic lattice and `Cs^(o+)` ion in the void (at body centre).
For bcc,
`(2r_(Cs^(o+)) + r_(Br^(ɵ)) = sqrt(3)a`
`2(1.69 + 1.95) = sqrt(3)a rArr a = 4.2 Å`