How do you tell these types of substances apart? (simply chemistry)?

Remember that elements make up compounds.

Refer to a Periodic Table to look for individual elements, such as that provided in my source list.

An element is the simplest form anything can be when found in nature. So, if we have iron, iron's chemical name is Fe. Fe is an element on the Periodic Table.

A compound contains one or more elements. So, if we have rust, rust is made up of iron + oxygen, and its chemical formula is Fe2O3. Fe and O are both elements on the Periodic Table, thus they are elements by themselves, but together they form a compound.

An atom is the simplest unit of nature. (Other than the theoretical strings of string theory and quantum physics, but that's far too technical for this case.)

And a molecule is made up of one or more atoms of the given elements.

So, for #1, you have H2O-that's water. H2O has 2 atoms of Hydrogen for every 1 atom of Oxygen, because Hydrogen is an element and Oxygen is an element, but when chemically combined they create a compound. H2 is a MOLECULE, because it has 2 Hydrogen atoms that are bonded together, but overall, H2O is a compound.

#2. HF= Hydrogen Fluoride, H + F chemically bonded. Here we have one atom of each element, H and F, but together they create one compound, HF. HF is one molecule.

#3. CO= Carbon Monoxide, C + O chemically bonded. This is the same situation as in #2. We have one compound, and it's a molecule.

#4. C6O= a compound, molecule.

#5. Cl2= an element, but a molecule of it because it's 2 atoms of Chlorine bonded together.

#6. Br2= an element as well, and a molecule as well, for the same reason as #5.

All of those are molecules (discrete entities consisting of more than one atom).

As for element v. compound, is there one kind of atom (element) or more than one kind of atom (compound)? 1, 2, and 3 are compounds and 4, 5, and 6 are elements.

1...H2O is a molecule of a compound of water.

2...HF is a molecule and compound of Hydrogen Fluoride.

3...CO is a molecule and compound of Carbon Monoxide.

4...C60 is a ball shaped elemetal molecule of 60 carbon atoms known as a 'Fullerene'.

5...Cl2 is diatomic pure elemental molecule of two Chlorine atoms

6...Br2 is diatomic pure elemental molecule of two Bromine atoms

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