How many molecules of neon are associated with a #75*L# volume of neon gas?
The question should have specified a temperature. I am going to assume that the gas is at room temperature,
We know that at room temperature and pressure,
We assume (reasonably) that
Thus the number of moles of
But by definition,
What is the mass of this quantity of neon gas?
(Neon gas is a monatomic molecule).
See also here.