What is the mass ratio of ethylene glycol $(C_2H_6O_2, \text{molar mass} = 62 g/mol)$ required for making $500 g$ of $0.25 m$ aqueous solution and $250 mL$ of $0.25 M$ aqueous solution?

$2 \ g$ of substance $A$ is added to $18 \ g$ of water to form a solution. Calculate the mass percentage of the solute. (in $\%$)

If $25 \ mL$ of $0.25 \ M$ $NaCl$ solution is diluted with water to a volume of $500 \ mL$,the new concentration of the solution is (in $M$)

$4.5 \ g$ of compound $A$ $(MW = 90)$ was used to make $250 \ mL$ of its aqueous solution. The molarity of the solution in $M$ is $x \times 10^{-1}$. The value of $x$ is ............ (Rounded off to the nearest integer)

If the density of some lake water is $1.25\, g\, mL^{-1}$ and contains $92\, g$ of $Na^{+}$ ions per $kg$ of water,calculate the molality of $Na^{+}$ ions in the lake. (in $, m$)

What is meant by mass percentage $( \% w/w )$?