Extensive Property:

An extensive property is a physical property of a system that depends on the amount of substance present in the system. In other words, extensive properties are additive and scale with the size or amount of the system. The value of an extensive property changes when the size or amount of the system changes.

Explanation:

Out of the given options, the correct answer is option 'B' - Entropy.

Entropy is a measure of the disorder or randomness of a system. It is a thermodynamic property that quantifies the number of microscopic configurations that a system can have. Entropy is an extensive property because it depends on the size or amount of the system.

Comparison with Other Options:

a) Specific Heat Capacity:
Specific heat capacity is the amount of heat energy required to raise the temperature of a substance by a certain amount. It is an intensive property because it does not depend on the amount of substance present. The specific heat capacity of a substance remains the same regardless of the size or amount of the substance.

b) Entropy:
As mentioned earlier, entropy is an extensive property as it depends on the amount of substance present in the system. If the system size or amount changes, the entropy of the system will also change proportionally.

c) Temperature:
Temperature is an intensive property because it does not depend on the amount of substance present. The temperature of a substance remains the same regardless of the size or amount of the substance.

d) Refractive Index:
Refractive index is a measure of how light propagates through a medium. It is an intensive property because it does not depend on the amount of substance present. The refractive index of a substance remains the same regardless of the size or amount of the substance.

Conclusion:

Among the given options, entropy is the only extensive property. It is a thermodynamic property that depends on the amount of substance present in the system. The other options, specific heat capacity, temperature, and refractive index, are intensive properties that do not depend on the amount of substance present.