The $\% \ w/V$ unit is used in which branch of science?

Which of the following statements is correct regarding the mole fraction of components in a solution?

Two solutions of a substance (non-electrolyte) are mixed in the following manner: $480 \ mL$ of $1.5 \ M$ first solution $+ 520 \ mL$ of $1.2 \ M$ second solution. What is the molarity of the final mixture $.......... \ M$.

The density of a solution containing $13 \%$ by mass of $H_2SO_4$ is $1.09 \ g/mL$. The molarity and normality of the solution are respectively :-

The mole fraction of a solute in a $100$ molal aqueous solution is $.......... \times 10^{-2}$ (Round off to the nearest integer). [Given: Atomic masses: $H = 1.0 \ u$,$O = 16.0 \ u$]

What is the sum of the mole fractions of all the components in a solution?