Question

the mass of nickel hydroxide that is dissolved in 225 mL of a saturated solution is

Answer 1

I think you might be missing some information..

Answer 2

you need to know the Ksp, from there you can find it's molar solubility, then you can scale it to 225 mL then convert to mass

Answer 3

any good text will have a table of KSP values, Ni(OH)2 probably has a very low KSP, so @aaronq is correct, find the maximum concentrations from KSP, then scale down to 225mL