Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R
Assertion A: In an Ellingham diagram, the oxidation of carbon to carbon monoxide shows a negative slope with respect to temperature.
Reason R: CO tends to get decomposed at higher temperature.
In the light of the above statements, choose the correct answer from the options given below

Solution

Chemistry ma’am · 4 steps

Count the gas moles: one mole of O₂ gives two moles of CO, so entropy rises and the line goes down.

1. Slope of a line. Each line in an Ellingham diagram plots Δ G° against T. Since Δ G° = Δ H° - TΔ S°, the slope of the line is -Δ S°.

   2C(s) + O₂(g) → 2CO(g) Δ n_(gas) = 2 - 1 = +1

2. Check Assertion A. Gas moles go up from 1 to 2, so Δ S° is positive and the slope -Δ S° is negative. The C to CO line falls as temperature rises, so A is correct.
3. Check Reason R. A falling line means Δ G° for forming CO gets more negative at higher temperature. CO becomes more stable when it is hot, not less. CO breaks down (2CO → C + CO₂) only at lower temperatures, so R is not correct.
4. So. A is correct and R is wrong, which is option (a). This same falling line is why carbon can reduce almost any metal oxide at a high enough temperature.

The idea to keep. In an Ellingham diagram the slope is -Δ S°. Count gas moles: if they increase the line falls, if they decrease it rises, if they stay equal it is flat.

Answer from the NTA final answer key. Solution by PrepWiser.