What is boiling point? What is freezing point?

Calculate the solubility (in $\text{moles/litre}$) of a saturated aqueous solution of $Ag_3PO_4$ if the vapour pressure of the solution becomes $750 \ torr$ at $373 \ K$. (Assume vapour pressure of pure water at $373 \ K$ is $760 \ torr$ and density of water is $1 \ g/mL$)

For a solution formed by mixing liquids $L$ and $M$,the vapour pressure of $L$ plotted against the mole fraction of $M$ in solution is shown in the following figure. Here $x_L$ and $x_M$ represent mole fractions of $L$ and $M$,respectively,in the solution. The correct statement$(s)$ applicable to this system is(are)
$A$. Attractive intermolecular interactions between $L-L$ in pure liquid $L$ and $M-M$ in pure liquid $M$ are stronger than those between $L-M$ when mixed in solution
$B$. The point $Z$ represents vapour pressure of pure liquid $M$ and Raoult's law is obeyed when $x_L \rightarrow 0$
$C$. The point $Z$ represents vapour pressure of pure liquid $L$ and Raoult's law is obeyed when $x_L \rightarrow 1$
$D$. The point $Z$ represents vapour pressure of pure liquid $M$ and Raoult's law is obeyed from $x_L=0$ to $x_L=1$

Which of the following is $CORRECT$ with respect to the property mentioned against it?

The solubility product of a sparingly soluble $AB_2$ salt is $2.56 \times 10^{-4} \ M^3$ at $25^{\circ} C$. The $K_f$ of water is $1.8 \ K \ kg \ mol^{-1}$. The depression in freezing point of a saturated solution of $AB_2$ is (in $K$)

An aqueous solution of urea: