What is the redox reaction? And how does the redox reaction happen inside batteries?

It is called a reduction-oxidation, oxide-reduction reaction, or simply as a redox reaction, any chemical reaction in which one or more electrons are transferred between the reactants

Redox battery is an example of both a Flow Battery and a two electrolyte system.In this case, it depends on two different active aqueous electrolytes of vanadium dissolved in sulfuric acid separated by a membrane at which ionic interchange takes place.

Thats my opinión though.

the answer would be c

we need the questions , i may then you.