PQ and `RS_(2)` are two sparingly soluble salts. Their solubility prodcts are equal and each equal to `4.0xx10^(-18)`. Which salt is more soluble?

Explanation

`underset(s)(PQ)tounderset(s)(P)+underset(s)(Q)`
`K_(sp)=s^(2)`
`4xx10^(-18)=s^(2)`
Solubility s `=2xx10^(-9)`
`underset(s)(RS_(2))tounderset(s)(R)+underset(s)(2S)`
`K_(sp)[R][2S]^(2)`
`=[s][2s]^(2)=4s^(3)`
`4s^(3)=4xx10^(-18)`
`s^(3)=(4xx10^(-18))/4=1xx10^(-18)`
`s=1xx10^(-5)` mole `L^(-1)`
`:.RS_(2)` is more soluble.