$3.1 \ g$ of a compound,'$X$' (molar mass $= 62 \ g \ mol^{-1}$) is dissolved in $19.5 \ g$ of other compound,$Y$ (molar mass $= 78 \ g \ mol^{-1}$). The ratio of mole fractions of $X$ and $Y$ in the solution is

$50 \ g$ of a substance is dissolved in $1 \ kg$ of water at $90^{\circ} C$. The temperature is reduced to $10^{\circ} C$. The density is increased from $1.1 \ g \ cm^{-3}$ to $1.15 \ g \ cm^{-3}$. What is the $\%$ change of molarity of the solution?

Concentrated $HCl$ is $10 \,N$. How can $1000 \,cc$ of $1 \,N \,HCl$ be prepared by dilution?

Air is an example of a solution of

The mole fraction of glucose $(C_{6}H_{12}O_{6})$ in an aqueous binary solution is $0.1$. The mass percentage of water in it,to the nearest integer,is $....$.

The molality of $648 \ g$ of pure water is .................. $m$.