Between which of the following
atoms is a covalent bond most
likely to occur?
a. calcium and lithium
b. sodium and fluorine
c. nitrogen and oxygen
d. helium and argon

The bond shared between Oxygen and Nitrogen is the covalent bond.

Option C

The bond formed between oxygen and nitrogen atom is due to the sharing of electrons between the two atoms. The electronegativity difference between the nitrogen and the oxygen atom is not enough to cause an ionic interaction between them. Hence, they are incapable to form an ionic bond.

For eg-

In this compound, nitrogen atom forms a double bond (which is a covalent double bond) with one atom of oxygen and a coordinate bond with the other atom of oxygen.

a. energy is absorbed in the reaction.

if in a given reaction the energy of products is greater than the energy of reactants it means that reaction is endothermic and during the reaction, the energy is absorbed by reactants. in an endothermic reaction, the products have more stored chemical energy than the reactants. and in this reaction the reactants are more stable than products before the compounds with less energy are always more stable.