Which sample contains the least number of atoms: #"2 g Ar; 2 g C; 2 L He; 2 L dihydrogen gas"#?
Which question does you want answered?
Clearly the last option is the most suitable, and most safe:
The resultant sodium nitrate could be crystallized from solution.
The other options involve addition of sodium to water, or acid, which would not be the safest exercise.
If you want to know which of the following contains LEAST amount of atoms, i.e. out of
In each case,
The least number of atoms is expressed in the sample of argon gas. Do you agree?