If atoms are removed from half of the edge-centred `OV_(s)` in `RbBr`, then the molecular formula of unit cell is

Options

A. `Rb_(2)Br_(2)`
B. `Rb_(1.5)Br_(3)`
C. `Rb_(2.5)Br_(4)`
D. `Rb_(4)Br_(2.5)`

Answer

C

Explanation

`Br^(ɵ)` in closest packed structure (e.g., fcc or ccp).
`:.` Number of `Br^(ɵ) = 4` (corner `+` face centre `= 1 + 3 = 4`).
Number of alternate `OVs = 6 xx (1)/(4)` (Edge center share)
`= (3)/(2) = 1.5`
Number of `Rb^(o+)` intially `=` Edge centre `+` body centre
`= 12 xx (1)/(4) + (1)/(1) = 4`
Number of `Rb^(o+)` ion left `= 4 - 1.5 = 2.5`
thus, formula is `Rb_(2.5)B_(4)`.