The molarity of pure water at $4\,^{\circ}C$ is ............... $M$.

The molarity of the solution obtained by mixing $800 \ mL$ of $0.5 \ M$ $HCl$ and $200 \ mL$ of $1 \ M$ $HCl$ will be ....... $M$.

If the molality of an aqueous solution is $m$ and the mole fraction of the solute is $y$,which of the following relations is correct?

$V_1 \ \text{c.c.}$ of a solution having molarity $M_1$ is diluted to have molarity $M_2$. The volume of water required to be added will be $:-$

The molarity of the solution prepared by dissolving $6.3 \ g$ of oxalic acid $(H_{2}C_{2}O_{4} \cdot 2H_{2}O)$ in $250 \ mL$ of water in $mol \ L^{-1}$ is $x \times 10^{-2}$. The value of $x$ is ..... . (Nearest integer)
[Atomic mass : $H: 1.0, C: 12.0, O: 16.0]$

$A$ 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.