Which of the following pairs of ions would be expected to form a precipitate when their dilute solutions are mixed?

Assign $A$,$B$,$C$,$D$ from the given type of reaction.
$BaCO_3 \downarrow + CO_2 + H_2O \longrightarrow Ba(HCO_3)_2$

The $K_{sp}$ of $Ag_2CrO_4$ is $1.1 \times 10^{-12}$ at $298 \ K$. The solubility (in $mol/L$) of $Ag_2CrO_4$ in a $0.1 \ M \ AgNO_3$ solution is

If the solubility of $Mg(OH)_2$ is $x \ mol/L$,then its solubility product $(K_{sp})$ is equal to .....

The minimum volume of water required to dissolve $0.1 \ g$ of lead $(II)$ chloride to get a saturated solution ($K_{sp}$ of $PbCl_2 = 3.2 \times 10^{-8}$; atomic mass of $Pb = 207 \ u$,$Cl = 35.5 \ u$) is......$L$

Assign $A, B, C, D$ from the given type of reaction.
$Ca(OH)_2 + 2HF \longrightarrow CaF_2 \downarrow + 2H_2O$