A covalent bond is formed when: a. two nonpolar molecules associate with each other in a polar environment. b. a positively charged particle is attracted to a negatively charged particle. c. one atom gives up electrons to another atom. d. two atoms share electrons. e. two polar molecules associate with each other in a nonpolar environment.

D. two atoms share electrons.

Explanation:

Chemical bonds are very important in chemical reactions. Examples of chemical bonds include electrovalent, covalent etc.

Covalent bonds deals with sharing of electron by two atoms. A common example is that of H2O( Water) in which the Hydrogen atoms share their electrons with the oxygen and the oxygen also shares its own electrons with the hydrogen in a mutual manner.

the answer to this question is 3.