As much
a) Coal atoms as as Oxygen atoms. I guess this is CO2. (Climaxed)
Not coal (that's what you mine) but carbon (the element). You are told there is the same number of atoms of both in a molecule, so CO
2 is out of the question, as it contains two times more oxygen.
b) 2x more Oxygen atoms as Coal atoms. I think this is (Columnist)
No idea what is (Columnist), just like I hae no idea what you meant by (Climaxed) earlier.
Fast chemical reactions (For example candle burning?)
Not bad.
Slow chemical reactions (Believe me I have no idea)
Iron fence that I put here 10 years ago is still standing, but it won't survive much longer.
H-O-H is a structural formula - it tries to show how the atoms are organized in space (in a simplified way). H
2O is just a composition of the molecule. The more complicated the molecule, the easier it is to write formula that reflects its composition, but not the arrangement of atoms.