Which of the following will have the highest freezing point $(F.P.)$ at one atmosphere?

Two elements $A$ and $B$ form compounds with molecular formulas $AB_2$ and $AB_4$. When $1 \ g$ of $AB_2$ is dissolved in $20 \ g$ of $C_6H_6$,the freezing point decreases by $2.3 \ K$. When $1 \ g$ of $AB_4$ is dissolved in $20 \ g$ of $C_6H_6$,the freezing point decreases by $1.3 \ K$. The molal depression constant for benzene is $5.1 \ K \ kg \ mol^{-1}$. Calculate the atomic weights of $A$ and $B$.

Calculate the cryoscopic constant $(K_f)$ of a solvent when $2.5 \ g$ of a solute is dissolved in $35 \ g$ of the solvent,which lowers its freezing point by $3 \ K$. (Molar mass of the solute is $117 \ g \ mol^{-1}$)

Calculate the freezing point of a solution prepared by dissolving $1.8 \ g$ of glucose $(C_6H_{12}O_6)$ in $500 \ g$ of water. The $K_f$ value for water is $1.86 \ K \ kg \ mol^{-1}$. (in $K$)

$40 \ g$ of glucose (Molar mass $= 180 \ g \ mol^{-1}$) is mixed with $200 \ mL$ of water. The freezing point of the solution is $..... \ K$. (Nearest integer)
[Given : $K_{f} = 1.86 \ K \ kg \ mol^{-1};$ Density of water $= 1.00 \ g \ cm^{-3};$ Freezing point of water $= 273.15 \ K$]

$6 \ g$ urea is dissolved in $1 \ kg$ solvent. The value of $(T_1 - T_2)$ will be .......... $^\circ C$. $(K_f = 2 \ kg \ K \ mol^{-1})$