How many hydrogen molecules are in h2

two

Explanation:

The symbol “H” means the hydrogen atom; “2H” means two hydrogen atoms that do not make a molecule: they are just two separate (individual) atoms; “H2” means the hydrogen molecule (two hydrogen atoms that came together, sharing their electrons); “2H2” means two separate hydrogen molecules.

c is the answer because when something is left after something evaporates that shows the chemical change.