The process that occurs when two equivalent forms of a compound are in equilibrium is

A.

Isotopy

B.

Resonance

C.

Isomerism

D.

Reforming

Correct answer is B

Resonance involves two forms of a compound.
Isomerism involves two or more forms of an element.
Reforming involves the rearrangement of molecule.

This deals with a two forms of a molecule where the chemical connectivity is the same but the electrons are distributed differently around the structure.