Which of the following is a physical change? burning a piece of wood rust forming on an iron fence sawing a piece of wood in half a copper roof changing color from orange to green

Sawing the piece of wood in half is a physical change,
because no new substances are formed that weren't there
before the sawing.

Burning wood produces carbon monoxide and carbon dioxide
that weren't there before the burning.  That's a chemical change.

Rust forming on iron is iron oxide that wasn't there before the
rusting.  That's a chemical change.

The green that appears on copper is copper oxide that wasn't
there before the green appeared.  That's a chemical change.