At $25\,^oC$, the solubility product of $Mg(OH)_2$ is $1.0\times10^{-11}$. At which $pH$, will $Mg^{2+}$ ions start precipitating in the form of $Mg(OH)_2$ from a solution of $0.001\, M\, Mg^{2+}$ ions?

The concentration of sulphide ion in $0.1$ $M$ $HCl$ solution saturated with hydrogen sulphide is $1.0 \times 10^{-19} \,M .$ If $10$ $mL$ of this is added to $5$ $mL$ of $0.04$ $M$ solution of the following: 

$FeSO_{4},$ $MnCl_{2},$ $ZnCl_{2}$ and $CdCl _{2}$ in which of these solutions precipitation will take place?

Given $K_{s p}$ for $FeS =6.3 \times 10^{-18},$ $MnS =2.5 \times 10^{-13}, ZnS =1.6 \times 10^{-24},$ $CdS =8.0 \times 10^{-27}$

Solid $Ba(NO_3)_2$ is gradually dissolved in a $1.0 \times 10^{-4}\, M$  $N_2CO_3$ solution. At what concentration of $Ba^{2+}$ will aprecipitate begin to form? ($K_{sp}$  for $BaCO_3 = 5 .1 \times 10^{-9}$)

There are equal volume of $0.02$ $M$ $CaC{l_2}$ and $0.00004$ $M$ $N{a_2}S{O_4}$ solution are mixed will a precipitation of $CaS{O_4}$ ? ${K_{sp}} = 2.4 \times {10^{ – 5}}$

The concentration of $500$ $ML$ $NaOH$ solution is $0.02$ $M$. How many grams of $FeS{O_4}$ added in this solution for precipitation of $Fe{\left( {OH} \right)_2}$ ? The ${K_{sp}}$ of $Fe{\left( {OH} \right)_2}$ is $1.5 \times {10^{ – 15}}$. Molecular mass of $Fe{\left( {OH} \right)_2}$ is $ 152$ $g$ $mol^{-1}$ )