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

The molarity of a solution of $Na_2CO_3$ having $10.6 \ g$ in $500 \ mL$ of solution is ......... $M$.

Which of the following statements is correct?
$(1)$ Molarity is the number of moles of solute in one liter of solution.
$(2)$ The normality and molarity of a sodium carbonate solution are the same.
$(3)$ The number of moles of solute dissolved in $1000 \ g$ of solvent is defined as molality $(m)$.
$(4)$ The ratio of the mole fractions of solute and solvent is equal to the ratio of their respective moles.

Which of the following solutions has the highest normality?

Mole fraction of solute in its $2$ molal aqueous solution is

Normality $N$ of a solution is equal to