Which of the following will have the lowest vapour pressure?

$9 \ g$ anhydrous oxalic acid (mol. $Wt. = 90$) was dissolved in $9.9 \ moles$ of water. If vapour pressure of pure water is $P_1^o$,the vapour pressure of solution is (in $P_1^o$)

The vapour pressure of a solvent decreases by $2.5 \ mm \ Hg$ by adding a solute. What is the mole fraction of solute? (Vapour pressure of pure solvent is $250 \ mm \ Hg$)

The vapour pressure of a solvent decreases by $20 \ mm$ of $Hg$ when a non-volatile solute is added to the solvent. The mole fraction of the solute in the solution is $0.5$. What should be the mole fraction of the solvent for the decrease in the vapour pressure to be $10 \ mm$ of $Hg$?

At $300 \ K$,the vapor pressures of two pure liquids $A$ and $B$ are $150 \ mm \ Hg$ and $100 \ mm \ Hg$,respectively. If the mole fractions of $A$ and $B$ in the solution are equal,then the mole fraction of $B$ in the vapor phase at the same temperature is:

Relative lowering in vapour pressure of a solution containing a non-volatile solute is the ratio of: