What fact about elements would explain why two elements would bond with the same element in the same proportion?

The elements are found in the same column on the periodic table.

The dispersed phase is liquid and dispersed medium in milk is liquid

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