Correct Answer - C
Diamond -`sp^(3)` , no `pi`-bond character and `C-C` bond length=`154` pm
graphite -`sp^(2)`, aromatic and `pi` electrons are delocalised and `C-C` bond length =`141.5` pm
fullerene-`sp^(2)`, not so good delocalisation and there are two types of bond length. `C-C` bond length decreases as compared with diamond but is more than of graphite. Bond lengths are `143.5` pm and `138.3` pm.