The number of units,which are used to express the concentration of solutions from the following,is $.......$ Mass percent,Mole,Mole fraction,Molarity,ppm,Molality.

Find out the mole fraction of methanol in a $5.2 \ m$ aqueous solution of methanol.

The number of moles of a solute in its solution is $20$ and the total number of moles is $80$. The mole fraction of the solute is:

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

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? $(N=14 \ u, O=16 \ u, H=1 \ u)$

The unit of mole fraction is: