Calculate the mass of urea $[NH_2CONH_2]$ required in making $2.5 \ kg$ of $0.25 \ m$ aqueous solution. (in $g$)

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 : $H: 1.0, C: 12.0, O: 16.0]$

The density of '$x$' $M$ solution ('$x$' molar) of $NaOH$ is $1.12 \ g \ mL^{-1}$. While in molality,the concentration of the solution is $3 \ m$ $(3 \ molal)$. Then '$x$' is.
(Given: Molar mass of $NaOH$ is $40 \ g \ mol^{-1}$)

What will be the molarity of a solution containing $5 \ g$ of sodium hydroxide in $250 \ mL$ solution?

The number of moles of $KCl$ in $1000 \ mL$ of $3 \ M$ solution is

The unit of mole fraction is: