$20 \, mL$ of $0.5 \, M \, HCl$ is mixed with $30 \, mL$ of $0.3 \, M \, HCl$. The molarity of the resulting solution is $......... \, M$.

Which of the following concentration factors changes with temperature?

$A$ sample of drinking water is severely contaminated with chloroform $(CHCl_3)$. $CHCl_3$ is considered 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.

Which of the following solutions has the highest normality?

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

What is the molarity of a solution containing $0.8 \ g$ of $NaOH$ (molar mass $40 \ g \ mol^{-1}$) in $150 \ cm^{3}$ of water?