For the equilibrium `CuSO_(4)xx5H_(2)O(s)hArrCuSO_(4)xx3H_(2)O(s) + 2H_(2)O(g)`
`K_(p) = 2.25xx10^(-4)atm^(2)` and vapour pressure of water is `22.8` torr at 298 K. `CuSO_(4)` . `5H_(2)O(s)` is efflorescent (i.e., losses water) when relative humidity is :

Options

A. less than `63.3%`
B. less than `50%`
C. less than `66.6%`
D. above `66.6%`

Answer

B

Explanation

`CuSO_(4)` . `5H_(2)O(s)hArrCuSO_(4)` . `3H_(2)O(s) + 2H_(2)O(g)`
`K_(p) =2.25xx10^(-4)`
`K_(p) = P^(2)H_(2)O =2.25xx10^(-4)`
`pH_(2)O = 1.5xx10^(-2)`
Vapour pressure `=(22.8)/(760) = 3xx10^(-2)`
R.H. `=(P_(H_(2))O)/(V.P.)xx100=50%`
Therefore, (b) option is correct.