These are a couple of examples of things that retail staff may be expected to get involved with, and they'll be keen to see how much additional training they might need to provide.
The atmosphere is a mixture of several gases. Nitrogen is the most abundant gas in the atmoshere and oxygen is next to it. It is 78% in the atmosphere and 21% is oxygen. Remaining 1% is all other gases like argon, hydrogen, neon, etc...