What is the oxidation state of Fe in Fe(CO)5
CO is a ligand, and its oxidation value is zero, so following the rules, ....
the CO ligand is neutral - it has a 0 charge.
So, Fe(CO)5 is neutral, and the Fe atom has an OX# of zero.
This is a very odd question for high school students, as ligand bonding is not normally served in beginning chemistry.