If `CuSO_(4)`.`5H_(2)O_((s))hArrCuSO_(4)`.`3H_(2)O_((s)) + 2H_(2)O_((l)) K_(p) = 1.086xx10^(-4) atm^(2)` at `25^(@)C`. The efflorescent nature of `CuSO_(4)`.`5H_(2)O` can be noticed when vapour pressure of `H_(2)O` in atmosphere is

Options

A. `gt7.29` mm
B. `lt7.92` mm
C. `ge7.92` mm0
D. None

Answer

B

Explanation

An efflorescent salt is one that loses `H_(2)O` to atmosphere. For the reaction
`CuSO_(4)`.`5H_(2)O(s)hArrCuSO_(4)`.`3H_(2)O(s) + 2H_(2)O_((I))`
`K_(p) = (P'_(H_(2)O)^(2)) = 1.086xx10^(-4)`
`P'_(H_(2)O) = 1.42xx10^(-2)` atm = `7.92` mm
`.:` If `P'_(H_(2)O)` at `25^(@)C lt 7.92` mm only, then reaction will proceed in forward direction.