a) Burning of fire cracker is a chemical change.  It produces heat, light & sound and it is irreversible.

b) Germination of seed is a chemical change because in chemical change new substance will be formed.  Seeds grows into a plant or tree and the character’s  and appearance changes.

c) Coal formation is a chemical change, coal is a fossil fuel.  It is formed by dead remains of living organisms.  It takes millions of years to form. It is entirely a new substance.