The number of moles of a solute in its solution is $20$ and the total number of moles is $80$. The mole fraction of the solute is:

The amount of water that should be added to $500 \, mL$ of $0.5 \, N$ solution of $NaOH$ to give a concentration of $10 \, mg$ per $mL$ is (in $, mL$)

Molar concentration $(M)$ of any solution $=$

When $100 \ mL$ of $0.3 \ N$ $HCl$ solution is mixed with $200 \ mL$ of $0.6 \ N$ $H_2SO_4$ solution,what is the normality of $H_2SO_4$ in the final mixture?

If the concentration of $Al^{3+}$ in an aqueous solution of $Al_2(SO_4)_3$ is $0.28 \ M$,then the concentration of $(SO_4)^{2-}$ ion is ........... $M$.

$A$ sample of drinking water was found to be severely contaminated with chloroform,$CHCl_{3}$,supposed to be carcinogenic in nature. The level of contamination was $15 \ ppm$ (by mass).
$(i)$ Express this in percent by mass.
$(ii)$ Determine the molality of chloroform in the water sample.