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

$A$ solution of a solute in benzene has a molality of $X \ m$. If the mole fraction of the solute is $0.2$,what is the value of $X$?

Calculate the molarity of ethanol in a solution where the mole fraction of ethanol is $0.040$. (Assume the density of water is $1 \ g/mL$.) (in $M$)

$A$ sample of drinking water is found to be severely contaminated with chloroform $(CHCl_3)$,which is a suspected carcinogen. If the level of contamination is $15 \ ppm$ (by mass),express this in percentage by mass.

Molarity is:

The density of a nitric acid solution is $1.5 \ g \ mL^{-1}$. Its weight percentage is $68 \%$. What is the approximate concentration (in $mol \ L^{-1}$) of nitric acid? $(N=14 \ u, O=16 \ u, H=1 \ u)$