When a strip of magnesium is heated in air, the student records the following observations:
I. The strip glows with an intense white light.
II. The strip becomes brittle and crumbles into a white powder.
III. The crucible’s temperature rises noticeably.
IV. A faint cracking sound is heard.
Which observation provides the strongest direct evidence that a chemical change has taken place?
a) III only
b) II only
c) II and III only
d) I only