What is the most stable part of the periodic table of elements

If you’re talking about groups/families, the Noble Gases are the most stable because they all have a full valence shell

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