What is electrochemistry? A. the study of photons in chemistry
B. the study of electricity in chemistry
C. the study of charge particles in chemistry
D. the study of valence-electrons in chemistry

B. the study of electricity in chemistry

Explanation:

Electrochemistry is the study of chemical processes that cause electrons to move. This movement of electrons is called electricity, which can be generated by movements of electrons from one element to another in a reaction known as an oxidation-reduction ("redox") reaction.

B => Study of electricity in chemistry

Explanation:

Electrochemistry is the study of electricity associated with chemical oxidation-reduction reaction. It is divided into two distinct disciplines; electrolysis and Galvanic Process.

Electrolysis is a nonspontaneous process requiring an outside power source (typically a battery) to drive the chemical reactions. Applications include metal refining and generation of various gases (for collection) by chemical process.

Galvanic Process is a spontaneous chemical process generating electrical energy by taking advantage of the different properties of metals.  Applications include batteries for many devices such as flash lights (Leclanche dry cell), alkaline button batteries for hearing aids, automobile batteries (lead storage batteries), the H₂/O₂ Fuel Cell battery, etc.

In general,

Electrolysis => Uses electrical energy (batteries) to drive chemical reactions

or,

Galvanic Process => Using chemical reactions to generate electrical energy