The vapor pressure of pure $A$ is $10 \ torr$. When $1 \ g$ of $B$ is dissolved in $20 \ g$ of $A$ at the same temperature,the vapor pressure of the solution becomes $9 \ torr$. If the molar mass of $A$ is $200 \ g/mol$,the molar mass of $B$ is ............ $amu$.

The vapour pressure of ethanol $(C_2H_5OH)$ and methanol $(CH_3OH)$ at $298 \ K$ is $44.5 \ mm \ Hg$ and $88.7 \ mm \ Hg$ respectively. At the same temperature,an ideal solution is prepared by mixing $60 \ g$ of ethanol and $40 \ g$ of methanol. Find the mole fraction of methanol in the vapour state.

$9 \ g$ 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 $P_1^o$)

Among the following substances,the lowest vapour pressure is exerted by

How many grams of a non-volatile solute (molar mass $40 \ g/mol$) must be added to $114 \ g$ of octane to reduce its vapour pressure by $20\%$ (in $g$)?

The vapour pressure of pure benzene at a certain temperature is $200 \ mm \ Hg$. At the same temperature,the vapour pressure of a solution containing $2 \ g$ of a non-volatile,non-electrolyte solid in $78 \ g$ of benzene is $195 \ mm \ Hg$. What is the molecular weight of the solid?