Covalent bonds are formed between which kinds of elements?

Covalent bonds are formed when two nonmetals share electrons in order to achieve a stable electron configuration. Nonmetals typically have high electronegativities and tend to gain electrons to fill their outer shells, but in a covalent bond, they opt to share electrons rather than completely transfer them. This electron sharing allows both atoms to attain more stable electronic arrangements, often resembling the noble gases.

In contrast, metals tend to form ionic bonds with nonmetals as they are more likely to lose electrons. Two metals would typically bond through metallic bonding, characterized by a 'sea of electrons' rather than sharing. A metal and metalloid might have other bonding characteristics, but covalent bonding primarily occurs between nonmetals, making the choice of two nonmetals the correct answer.