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. `gt 7.92 mm`
B. `lt 7.92 mm`
C. `overset(gt)(lt) 7.92 mm`
D. none of these

Explanation

An efflorescent salt is one that loses `H_(2)O` at atmosphere.
For the reaction,
`CuSO_(4)*5H_(2)O_((s))hArrCuSO_(4)*3H_(2)O_((s))+2H_(2)O_((v))`
`K_(p)=(P'_(H_(2)O))^(2)=1.086xx10^(-4)`
`P'_(H_(2)O)=1.042xx10^(-2)atm=7.92 mm`