(5 x 10 4) + (2.5 x 10 2) =
2 x 10 2
12.5 x 10 2
0.5 x 10 6
5 x 106

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