If you have 3.0 liters of an unknown gas, at standard temperature and pressure conditions, then you can calculate what about that gas?

We assume it as an ideal gas therefore we can use the ideal gas equation to solve the problem. The ideal gas equation is expressed as PV = nRT. We are given the volume, temperature and pressure. Therefore, we can solve for the amount of the gas in moles.

n = PV / RT
n = 1.00(3L) / (0.08206 atm L/mol K ) 273 K
n = 0.1339 mol

The teacher is mostly talking about the distillation of a mixture

The atomic nucleus made up from protons (yellow) and neutrons (blue) and held together by nuclear forces. nuclear forces (also known as nuclear interactions or strong forces) are the forces that act between two or more nucleons. they bind protons and neutrons (“nucleons”) into atomic