This paper presents two expressions define the ideal gaseous mixture entropy via its components entropies, the components being in two different conditions after segregation. In one case the components have the mixture temperature and pressure, whereas in the second case they also have the mixture temperature but their own partial pressure. As follows of data analysis, the conditions under which the mixture entropy is equal to the sum of its components are derived. The complete analysis allows us to some controversies called “The Gibbs paradox”. Refs 4.