Given below are two statements: one is labelled as Assertion A and...

For line II $∆ S$ is more negative than line I. In the Ellingham diagram, a sharp change in slope of the line is observed for $Mg - MgO$ at $~ {1120}^{o}C$ because that is the boiling point of magnesium.

From diagram, $∆ {S}_{I} = ( {S}_{solid} ) - ( {S}_{solid} + {S}_{gas} ) ∆ {S}_{II} = ( {S}_{liquid} ) - ( {S}_{solid} + {S}_{gas} )$

There is a large increase in entropy associated with the change of state of magnesium.

So, both Assertion (A) and Reason (R) are true and (R) is the correct explanation of (A).