Which of these elements has atoms that would have the most difficulty forming a covalent bond with oxygen (O) ?

A. O

B. S

C. N

D. Ne

Sulphur and Nitrogen are both missing at least 1 electron in their outer orbits like oxygen. The stable state is 8 electrons in the outer orbit. There are all able to form covalent bonds by sharing electrons with other atoms. This works because they all want to gain electrons to stabilize their outer orbit with 8 electrons. Neon however, is a noble gas which already has 8 electrons in its outer orbit. So it would not want to form a covalent bond by sharing electrons with the O. That would destabilize it. So the answer is D