The percentage (by weight) of sodium hydroxide in a $1.25$ molal $NaOH$ solution is (in $\%$)

In $500 \ mL$ of $0.2 \ M \ NaCl$ solution,$1500 \ mL$ of $0.4 \ M \ MgCl_2$ solution is mixed. The only incorrect final concentration of ion is (assume volume to be additive)

Molality of an aqueous solution of urea is $4.44 \ m$. Mole fraction of urea in solution is $x \times 10^{-5}$. Value of $x$ is. . . . . . (integer answer)

Calculate the molarity of $NaOH$ solution prepared by dissolving $0.4 \ g$ of $NaOH$ in enough water to form $500 \ mL$ of the solution. (in $M$)

Calculate the mass of urea $(NH_2CONH_2)$ required in making $2.5 \, kg$ of $0.25 \, \text{molal}$ aqueous solution.

$63 \ g$ of a compound (Mol. Wt. $= 126$) was dissolved in $500 \ g$ of distilled water. The density of the resultant solution is $1.126 \ g / mL$. The molarity of the solution is: (in $M$)