Drag electrons back and forth until the molecule of oxygen (O2) is stable. Click Check to confirm your molecule is stable. How many pairs of shared electrons are there in a stable molecule of oxygen?

2 pairs (4 electrons)

Explanation:

In a molecule of oxygen there are 2 oxygen atoms. There are 6 electrons in the outer shells of oxygen atoms. When 2 oxygen atoms form a covalent bond they share their electrons. In a diagram this would be represented by the overlap of the two circles representing the outer shells of both oxygen atoms. If each oxygen atom 'puts forward' 2 electrons into the centre, then 4 will be shared overall for each atom, making both atoms have full outer shells of 8 electrons each. 4 electrons make 2 pairs, hence the answer.