Question

Water is made of two hydrogen atoms and one oxygen atom bonded together. Julia is describing how water undergoes a physical change when it boils. She says that the particles shift to be farther apart and that the oxygen and hydrogen separate. She also says that the total mass of the steam is the same as the initial water, and that heat energy was required to cause the change. She finishes her description by saying that the steam can be turned back into water if it is cooled.
what was her mistake?

Answer 1

Everything that Julia said is correct EXCEPT the words
"the Oxygen and Hydrogen separate".  They do not. 

The "particles" that she mentioned are water molecules,
each one composed of two Hydrogen atoms and one Oxygen
atom bonded together.  THOSE are the particles that shift to be
farther apart, but the Hydrogen and Oxygen in each one remain
bonded together.

Julia gets 30 ounces of merit badges, out of a possible quart.