[cerraval]

What is the molar fraction of O2, CO2 and N2 in a 0.2 mol O2,0.3 mol CO2,0.7 mol N2 gas mixture?

Thanks in advance, that's very important to me. I'd love to know a lot more than I know but I'm new to these issues so, can anyone  help me, please?

{MOD Edit - useful title}

[Corribus]

Well they give you the number of moles of each gas in the mixture, so this is pretty straightforward. At this forum, showing your work is required to receive help. So why don't you describe what you think the answer is, and then we can lend assistance.

[Borek]

To add to what Corribus wrote: start with the definition.