Gibbs paradox in statistical mechanics is related to

Explanation:

• The classical Gibbs paradox concerns the entropy change upon mixing two gases.
• Whether an observer assigns an entropy increase to the process depends on their ability to distinguish the gases.
• A resolution is that an “ignorant” observer, who cannot distinguish the gases, has no way of extracting work by mixing them.

So, a semi-classical derivation of the entropy that does not take into account the indistinguishability of particles, yields an expression for the entropy which is not extensive.