Attached please find a question which was given to us in an exam and which was marked wrong for me.

I formed two equations in order to solve this:

(2220KJ * moles of propane) + (2877KJ * moles of butane) = 654KJ ---> Equation 1

Total number of gases:
If 1 mole occupies 22.4dm3
? Occupies 5.6dm3

Thus total number of moles of gases = 0.25 moles

Thus,

moles of propane + moles of butane = 0.25 ----> Equation 2

For moles of propane I got the answer: 0.0993 moles while,
The number of moles of butane: 0.151 moles

Have I worked it out correctly or not?

It seems correct to me and your final answers were?

For moles of propane I got the answer: 0.0993 moles while,
The number of moles of butane: 0.151 moles

Read your question again, it asks for the mole fraction, not the number of moles of each :)

If you don't know that that means, you can use Google, which gives a good definition.

Yes I know and I worked that out. What I want to know is if the basis of m answer is good or not

I told you already that it was right, by saying that "It seems correct to me" :)

Thank you very much