`K_(sp)` of `Mg(OH)_(2)` is `1.8 xx 10^(-11)` at `30^(@)C` . Its molar solubility is `…..........` at pH `=5`

Options

A. `1.8 xx 10^(-11)M`
B. `1.8 xx 10^(-9) M`
C. `1.34 xx 10^(-54)M`
D. `1.8 xx 10^(-7)M`

Answer

D

Explanation

`Mg(OH)_(2) hArr Mg^(2+)+2OH^(-)`
`pH =12 implies pOH =2`
`:. [OH^(-)]=10^(-2)M`
`K_(sp)=[Mg^(2+)][OH^(-)]^(2)`
`1.8 xx 10^(-11) =s xx (10^(-2))^(2)`
`:. s=1.8 xx 10^(-7) M`