(d) : The empirical formula of chlorophyll a molecule is C55H72O5N4Mg. It has tadpole like configuration. It consists of a porphyrin head and a phytol tail. Porphyrin is a cyclic tetrapyrol structure, having a magnesium atom in the centre. In chlorophyll a, a methyl group (CH3) is attached to the third carbon in the porphyrin head.