Answer :
A physical change would be A. Sawing a piece of wood in half because it's still the same. It would be a chemical reaction if the color of the wood would've changed.
Answer:-
- Sawing of piece of wood in half.
→ Physical; it is because no chemical properties are changed. They are same, just change is seen physically.
- Burning of a piece of wood.
→ Chemical; it is because chemical changes are observed. Wood is converted into Carbon.
- Rust forming on an iron fence.
→ Chemical; iron looses it's chemical properties on rusting. Thus, it is a chemical change.
- A copper roof changing color from red to green.
→ Chemical; chemical change is observed.
Conclusion: Sawing a piece of wood in half is the answer.