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Answer :

Answer: Wood burning is chemical because they produce substances that are new chemical compounds. Water boiling is chemical and grass growing is physical. Rock being crushed to powder is just physical because its still the same chemical identity

Explanation:

Answer:

See below

Explanation:

Wood burns - chemical;  wood is converted to a ashes through combustion which is a chemical reaction

Water begins to boil - chemical;  when water is boiled, bonds are broken in the chemical formula of water

Grass grows - chemical;  Grass grows due to chemical changes within the grass cell.

Rock is crushed - physical;  The combustion of the rock has not change just the physical appearance.