You just chose the best answer, but there is a problem, because there are only 17 electrons in the summation. This can be explained because there is a "dimer".
 

Fe0            = 8e- (5-C5H5) = 5e- 2 x (CO)T = 4e- Fe-Fe       = 1e-                     18e-

The bonding between the two Fe atoms give the extra electron to get 18 electrons.

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