determine what substance the following is: pile of leaves *
a. element
b. compound
c. homogeneous mixture
d. heterogeneous mixture

I would think it is a heterogeneous mixture since it can't be an element since there are more than one type of atom, it can't be a compound since the leaves are not bonded together, and it can not be a homogeneous mixture since the leaves don't all blended together (the pile is not uniform) and you can distinguish all the different parts of the mixture.  It can be considered a heterogeneous mixture since the leaves are mixed together (along with other things like dirt) in a non-uniform way so that you can point out the parts of the mixture and it does not look like one thing.

I hope this helps.  Let me know in the comments if anything is unclear.