Which of the following pairs of ions when mixed in dilute solutions may give a precipitate?

The $K_{sp}$ value for $Gd(OH)_3$ is $2.7 \times 10^{-23}$. At what $pH$ will $Gd(OH)_3$ begin to precipitate? (Given: $\log 3 = 0.48$)

When equal volumes of the following solutions are mixed,precipitation of $AgCl$ $(K_{sp} = 1.8 \times 10^{-10})$ will occur only with:

$MY$ and $NY_3$,two nearly insoluble salts,have the same $K_{sp}$ values of $6.2 \times 10^{-13}$ at room temperature. Which statement would be true in regard to $MY$ and $NY_3$?

The solubility of $BaSO_{4}$ in water is $2.42 \times 10^{-3} \ g \ L^{-1}$ at $298 \ K$. The value of solubility product $(K_{sp})$ will be (Given molar mass of $BaSO_{4} = 233 \ g \ mol^{-1}$)

The solubility product $(K_{sp})$ values of $CuS$,$Ag_2S$,and $HgS$ are $10^{-31}$,$10^{-44}$,and $10^{-54}$ respectively. The solubilities of these sulphides are in the order: