When $7.1 \ g$ of $Na_2SO_4$ (molecular mass $142$) dissolves in $100 \ mL$ of $H_2O$,the molarity of the solution is $.........$ $M$.

The sum of the mole fraction of the components of a solution is

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

The quantity which changes with temperature is:

If a solution is $98\% \ H_2SO_4$ by weight and has a density of $1.8 \ g/mL$,its molarity is ....... $M$.

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