Molarity is defined as per liter.
moles
grams
atoms

Molarity is defined as moles per liter.

Explanation:

Molarity or also called molar concentration is defined as the number of moles of a solute that are dissolved in a volume. The molarity or molar concentration can be calculated with the following formula:

Molarity (M) =  number of moles of solute /Dissolution volume

The units for expressing molarity or molar concentration are moles/liter.

the ideal gas law equation is as follows

pv = nrt

where p - pressure

v - volume

n - number of moles

r - universal gas constant

t - temperature

so if the pressure, volume and temperature are already known

we are left with n and r

since r is the universal gas constant that has a known fixed value then r too is known

so we are left with 'n'

once we know temperature volume and pressure

we can find the number of moles of gas present using the ideal gas law equation

this is not my own answer, this is an answer for the same question by the user blahblahmali. i do not claim ownership of this account.