6. 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 hot sun, it was slightly longer. Which sentence best describes
what happened to the iron atoms after the bar was left in the hot sun?

A - the number of atoms increased
B- the size of the atoms increased
- the space between each atom increased
D- some of the atoms began to melt and spread out further in the bar