Calculate the mass percentage of $3 \ g$ of solute $A$ dissolved in $18 \ g$ of water. (in $\%$)

The molarity of pure water is $......$

$A$ 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.

If $1 \ M$ and $2.5 \ L$ $NaOH$ solution is mixed with another $0.5 \ M$ and $3 \ L$ $NaOH$ solution,then the molarity of the resultant solution will be $........ \ M$.

The density of a $10.0\% \, w/w$ aqueous solution of $KCl$ is $1.06 \, g \, cm^{-3}$. The molarity of this solution is ........

$4.5 \ g$ of compound $A$ $(MW = 90)$ was used to make $250 \ mL$ of its aqueous solution. The molarity of the solution in $M$ is $x \times 10^{-1}$. The value of $x$ is ............ (Rounded off to the nearest integer)