Answer
Physical changes: Cooling of liquid mercury to -400C where it solidified
Chemical changes: mercury oxide produces mercury and oxygen when heated; wood burning into oxygen.
Work Step by Step
Physical changes: Cooling of mercury until it is solidified is a physical change as the substance ( mercury) changes the form of the matter ( from liquid to solid) but it retains its chemical identity (as it remains mercury).
Chemical changes: mercury dioxide is transformed into two new kinds of matter: mercury and oxygen. As new substances are formed, this is a chemical change.
Wood burning into oxygen is a chemical change as at the end of this process wood is transformed into new substances.
