A scientist is performing an experiment on a

powder. Which of the following is a sign that a chemical change has definitely occurred during his experiment?

The powder catches on fire.

The powder releases bubbles.

The powder heats up.

The powder breaks apart into smaller particles.

2 answers

a yes
b yes
c either
d no

c can be either. If it heats up because you built a fire under it that is a physical change. If it heats up because of the experiment being conducted it is a chemical change.
The answer is A :D