The metal oxide rectifier used for electrolytic process is placed along with the transformer:
(A) Inside the oil
(B) Outside the transformer but near to it
(C) Outside the transformer but far from it
(D) Half immersed in the oil

Hint
Metals react with oxygen to form metallic oxide while Non metals react with oxygen to form non metallic oxide. Metallic oxide are basic in nature while Non metallic oxides are acidic in nature.

Complete step by step answer
Metal oxides are well-known materials for the sensor and biosensor applications. In fact, the surface of metal oxides is a key factor for effective interaction with target molecules. Tailoring of the surface properties of metal oxide allows improving sensitive properties. A metal oxide rectifier used inside the transformer to provide reverse breakdown voltage. This type is commonly known as the metal-oxide varistor (MOV). Varistors are used as control or compensation elements in circuits either to provide optimal operating conditions or to protect against excessive transient voltages.
Option (A) is correct.

Note
A Metal Oxide Varistor (MOV) is a protection component used in power supply circuits that is powered directly from AC mains. It is used to protect the circuit from high voltage spikes by varying its resistance.