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 ∼1120∘C 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
(A)Both A and R are true but R is NOT the correct explanation of A
(B)Both A and R are true and R is the correct explanation of A✓ Correct
(C)A is false but R is true
(D)A is true but R is false
Answer: (B)
Solution
Both statements are true and R correctly explains A. In the Ellingham diagram, the slope of a line is determined by −ΔS (from ΔG=ΔH−TΔS). At approximately 1120°C, magnesium undergoes a phase change from solid to liquid. This phase transition involves a large change in entropy (ΔS becomes more negative when comparing solid Mg + gas O₂ → solid MgO versus liquid Mg + gas O₂ → solid MgO). The entropy change for the reaction involving liquid Mg is more negative than for solid Mg, causing a sharp change in the slope of the Ellingham line at the melting point of magnesium. Therefore, R correctly explains A.
JEE Main · 2023 · 12 Apr 2023 · Shift 1 · Single correct option
