Molarity is expressed as

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

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

What would be the molality of $20\%$ (mass/mass) aqueous solution of $KI$? (Molar mass of $KI = 166 \, g \, mol^{-1}$)

Some amount of dichloromethane $(CH_2Cl_2)$ is added to $671.141 \ mL$ of chloroform $(CHCl_3)$ to prepare a $2.6 \times 10^{-3} \ M$ solution of $CH_2Cl_2$ $(DCM)$. The concentration of $DCM$ is $......... \ ppm$ (by mass). Given: Atomic mass: $C = 12, H = 1, Cl = 35.5$; density of $CHCl_3 = 1.49 \ g \ cm^{-3}$.

Air is an example of a solution of