Final answer:
The correct answer is c. H2, is a diatomic molecule because it consists of two bonded hydrogen atoms but is not a compound since it's made of the same type of atom.
Step-by-step explanation:
The question requires understanding the difference between a molecule and a compound. H2O is a molecule and a compound since it contains two hydrogen atoms and one oxygen atom all chemically bonded together. The symbol H+ represents a hydrogen ion, which is not a molecule but an atom with a positive charge. The expression 2H indicates two separate hydrogen atoms, not bonded together, so it does not represent a molecule. Therefore, H2 is the answer; it represents a diatomic molecule of hydrogen, consisting of two atoms of the element that are chemically bonded together, but it is not a compound because it is composed of only one type of atom.