How many electrons are shared between two oxygen atom? 

4

The correct answer is option 1. 4.

When two oxygen atoms bond together to form a molecule of oxygen gas \((O_2)\), they each contribute one electron to a pair of electrons that is shared between them. This sharing of electrons occurs due to the overlap of the outermost electron orbitals of the oxygen atoms. Each oxygen atom needs two additional electrons to complete its outer shell, and by sharing two pairs of electrons, both oxygen atoms achieve a stable configuration resembling that of a noble gas.

So, in total, there are four electrons shared between the two oxygen atoms, resulting in a double covalent bond. This shared electron pair forms a strong bond that holds the oxygen atoms together in the oxygen molecule. Therefore, the answer is 4 electrons.