Coal releases carbon dioxide when burned. The reaction looks like this:
C(s)+O₂(g)→CO₂(g)
I hope this helps. Let me know in the comments if anything is unclear.
To calculate the average atomic weight, each exact atomic weight is multiplied by its percent abundance, then, add the results together. If the natural abundance of 63Cu is assigned x, the natural abundance of 65Cu is 1-x (the two abundance always add up to 1). So the solution is: (63)(x)+(65)(1-x) = 63.55, 63x+65-65x=63.55, x=0.725=72.5%. The natural abundance of 63Cu is 72.5%, that of 65Cu is 1-72.5%=27.5%.
The answer for this question is D.
