How many molecules are in 1L of O2 under the same conditions of temp and pressure?

[s3a]

I am really low on chemistry knowledge at the moment so I'd appreciate if somebody could show me the full solutions to this question because my answer guide only has the selected multiple choice letter listed.

Thanks in advance!

Question:
http://img522.imageshack.us/img522/7430/chemquest.jpg

P.S.
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[Russ]

I'm on my phone, so unfortunately I can't give you a worked solution. But the picture looks like it's a PV=nRT with some of them as constants.

Then you just need to convert 1L to cubic centimetres. Do you have the answer. At a guess, i'd go 4n.