The law formulated by Dr Nernst is:
A. First law of thermodynamics
B. Second law of thermodynamics
C. Third law of thermodynamics
D. Both (a) and (b)

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Hint: "Thermodynamics" implies the flow of heat.
It deals with energy changes accompanying all types of physical and chemical processes.
There are four laws of thermodynamics that give an idea about temperature, heat, work, and entropy.

Complete Step by Step Solution:
The laws of thermodynamics are helpful in the prediction of the feasibility or spontaneity of a process.
These laws are only applicable to substances in bulk not to individual atoms or molecules.

A. First law of thermodynamics
It states that energy can neither be developed nor be eradicated but can be transformed from one form to another.
Thus, the disappearance of one form of energy leads to the appearance of an equivalent amount of energy in some other form.
This law was not formulated by Dr Nernst.
So, A is incorrect.

B. Second law of thermodynamics
It states that the entropy of the universe increases for an irreversible process.
It remains constant for a reversible process.
Natural processes are spontaneous and irreversible.
For example, water flowing downwards spontaneously. The direction of flow cannot be reversed without any external assistance.

C. Third law of thermodynamics
It states that at the absolute zero temperature, the entropy of every substance may become zero and it does become zero in the case of a perfectly crystalline solid.
In a perfect crystal, at absolute zero temperature, there is a state of perfect order which means zero entropy.
We know that entropy is defined as the degree of disorders.
This law was given by Dr. Walther Nernst.
So, C is correct.

So, option C is correct.

Note: The first and second laws of thermodynamics are based on human experience and thus have no formal proof. The third law of thermodynamics was given by Walther Nernst, a German chemist.