Why are hydrogen and oxygen written as H2 and O2?

1. They are diatomic molecules.

2. All individual elements have the subscript 2.

3. To balance the equation.

The answer is 1, the elements are diatomic and both contain 2 atoms in the same element

If a hydrogen atom is neutral, it must also have  one electron. an oxygen atom (o) has an atomic number of eight (8). this means a neutral oxygen atom has eight protons and eight electrons. the element actium (ac) has an atomic number of 89, so it has 89 protons and 89 electrons in a neutral atom