Point defects in a metal sulfide

See the equilibrium of the defects of a metal sulfide MS with sulfur vapor at temperature 1,246 K. 

Express, according to the various equilibrium constants Ki and the pressure of di-sulfur vapor, the approximate expressions for the concentrations of the various point defects and consider the range of validity of these expressions in the pressure space. 

What range of pressures can we be satisfied with a Wagner approximation  

Substitute Sn ions for ions into the preceding metal sulfide with the concentration C = 0.15 at tenqterature 1,246 K and under the di-sulfur pressure of 0.1 mmHg. Compute the concentrations of the various defects. 

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