A human baby is born with one X chromosome and one Y chromosome. What
must be true about this baby?

Obviously it's a boy.

Explanation:

XY is a set of chromosome that shows that baby is a boy.

If, a set is XX then it's a baby girl.

answer is: c. the experiment shows that the red substance experienced a chemical change.

this is chemical change (chemical reaction), because two new substances are formed (metalig liquid and gas), the atoms are rearranged and the reaction is followed by an energy change.

this is example of chemical decomposition.

chemical decomposition (analysis) is the separation of a single chemical compound into its two or more elemental parts or to simpler compounds.  

chemical decomposition is opposite of chemical synthesis.