I really need anyone's help in chemistry

[leena babsail]

In chapter 5 :
when do we use L 22.4 and when do we use STP 1 atm and
T=273 ??
and why in Example 5.4 used this equation V=N . V ??
and do they mean by putting no number before the compound that it is a 1 mol ??
please i need answers tommorow is our exam
thankss