CO is not an element because CO is a Compound. Elements contain One capital and one lowercase letter. While Compounds contain two or more capital letters.
Answer:
which one you didnt explain or added attachment?
Example
H2SO4
H = 2 atoms
S = 32 atoms
O = 4 atoms
atomic mass :
H = 1 u.m.a
S =32 u.m.a
O= 16 u.m.a
H2SO4 = 1 x 2 + 32 x 1 + 16 x 4 = 98 g/mol
hope this helps!
A chemical symbol designates an element that belongs to the periodic table.
A chemical formula combines two or more symbols and it represents a chemical compound. We notice that the chemical symbols are followed oftenly by a subscript that represents the mole proprtions of next element.