Polarity is a measure of the uneven distribution of electron density within a molecule, resulting in a separation of charge.

Chlorophyll a and b are both pigments involved in photosynthesis, and their structures differ in the following ways:

* Chlorophyll a has a methyl group (-CH3) at the 3-position of the porphyrin ring.

* Chlorophyll b has a formyl group (-CHO) at the 3-position.

The formyl group (-CHO) in chlorophyll b is more polar than the methyl group (-CH3) in chlorophyll a. This is because the formyl group has a carbonyl group (C=O), which is highly polar due to the electronegativity difference between carbon and oxygen.

Therefore, the presence of the formyl group in chlorophyll b makes it more polar than chlorophyll a.