Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R
Assertion A : In the Ellingham diagram, a sharp change in slope of the line is observed for Mg → MgO at -1120oC Reason R: There is a large change of entropy associated with the change of state.
In the light of the above statements, choose the correct answer from the options given below
(1) Both A and R are true but R is NOT the correct explanation of A
(2) A is false but R is true
(3) A is true but R is false
(4) Both A and R are true and R is the correct explanation of A

Answer: Option 4
Solution: Assertion A is true because the Ellingham diagram is a graph that shows the variation of the standard free energy change (ΔG°) with temperature for the formation of oxides from the corresponding elements. The sharp change in slope for Mg → MgO indicates a change in the mechanism of the reaction, which is due to the change in the oxidation state of magnesium from 0 to +2.

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Reason R is also true because the change of state from solid Mg to gaseous MgO involves a large increase in entropy due to the increase in molecular randomness because of phase or state change due to melting or evaporation.

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