Consider the following statements: 1. The entropy of a pure crystalline substance at absolute zero temperature is zero. 2. the efficiency of a reversible heat engine is independent of the nature of the working substance and depends only on the temperature of the reservoirs between which it operates.  3. Carnot’s theorem states that of all heat engines operating between a given constant temperature source and a given constant temperature sink, none has a higher efficiency than a reversible engine Which of the above statements are correct?

Option 4 : 1, 2 and 3

The third law of thermodynamics or Nernst's theorem: The absolute entropy of a purely crystalline substance in complete internal equilibrium is zero at zero degrees absolute.

The consequences of the Second Law of Thermodynamics were proposed by Carnot and are called Carnot theorems.

Carnot Theorem 1: No heat engine operating between the two given thermal reservoirs can be more efficient than a reversible heat engine operating between the same two thermal reservoirs.

Carnot Theorem 2: All reversible heat engines operating between the two given thermal reservoirs have the same efficiency. The efficiency of a reversible heat engine does not depend on the working fluid, but depends only upon the temperatures of the reservoirs between which it operates.