Answer:
See below
Step-by-step 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.