How many pairs of electrons do two atoms of oxygen need to share to produce one molecule of O2?

2 pairs or 4

Explanation:

Oxygen atom belongs to the group 16 of the periodic table also known as the chalcogen group. Oxygen has atomic number of 8. This means it has 8 protons. Hence, for an electrically neutral oxygen atoms, there are 8 electrons.

These electrons are present in the first two shells. There are two electrons in the first shell also known as the K shell. There are 6 electrons in the valence shell of the oxygen atom which is also the L shell. These six valence electrons are the ones responsible for the chemical bonding with other elements.

As said earlier, oxygen atom has six electrons in its valence shell. This means to complete an octet configuration, there are two more electrons needed for it to achieve the needed stability. These two electrons can be obtained ionically or covalently. This depends on the other atom with which it is entering chemical combination with.

In the case of this question, we know it is another oxygen atom. This means each of these atoms will contribute 2 each to make up 2 pairs or 4 electrons which are then controlled by the nuclei of both atoms