Nate measured an iron bar. He put the iron bar in the hot sun. When he measured the bar after it had been in the sun, it was slightly longer. Which sentence best describes what happened to the iron atoms after the bar was left in the hot sun? Consider what happens to an iron bar when left out and exposed to sunlight and why it happens.
Evaluate the statements and select the one that best represents what happens.
Provide your reasoning in the text box provided.

The number of atoms increased.
The size of the atoms increased.
The space between each atom increased.
The air in the spaces between the iron atoms expanded.