Polysaccharides

Chitin is a complex polysaccharide made of N-acetylglucosamine, so it contains nitrogen.

A good storage material should stay in the cell for a long time without disturbing the working of the cell.
(2) Starch is chemically non-reactive: it has very few free reducing ends, so it does not take part in the reactions of the cell and can be stored safely for long periods.
(4) Starch is osmotically inactive: it is a large, insoluble polymer, so it does not change the osmotic concentration of the cell and does not draw water into it, even when stored in large amounts.
(1) is not a property of starch: because it is insoluble it is not easily translocated; carbohydrate is translocated mainly as sucrose.
(3) Being easily digested by animals is of no use to the plant as a storage property.
(5) Being synthesized during photosynthesis does not make it a good storage material.
So the properties that make starch useful as a storage material are (2) and (4).