If $138 \ g$ of ethanol is mixed with $72 \ g$ of water,the ratio of the mole fraction of alcohol to water will be ..........

$A$ sample of drinking water is found to be severely contaminated with chloroform $(CHCl_3)$,which is a suspected carcinogen. If the level of contamination is $15 \ ppm$ (by mass),express this in percentage by mass.

If the concentration of glucose $(C_{6}H_{12}O_{6})$ in blood is $0.72 \ g \ L^{-1}$,the molarity of glucose in blood is $..... \times 10^{-3} \ M$. (Nearest integer)
(Given: Atomic mass of $C=12, H=1, O=16 \ u$)

Given below are two statements: one is labelled as Assertion $A$ and the other is labelled as Reason $R$.
Assertion $A$: At $10^{\circ} C$,the density of a $5 \ M$ solution of $KCl$ is given. The solution is cooled to $-21^{\circ} C$. The molality of the solution will remain unchanged.
Reason $R$: The molality of a solution does not change with temperature as mass remains unaffected by temperature.
In the light of the above statements,choose the correct answer from the options given below:

The volumes of two $HCl$ solutions $A$ $(0.5 \, M)$ and $B$ $(0.1 \, M)$ to be mixed for preparing $2 \, L$ of $0.2 \, M \, HCl$ are

What is the mole fraction of the solute in a $1 \, m$ (molal) aqueous solution?