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

We need to evaluate statements about the Ellingham diagram.

Assertion A: "In an Ellingham diagram, the oxidation curve $$2C + O_2 \rightarrow 2CO$$ has a negative slope (goes downward with increasing temperature)."

This is TRUE. For the reaction $$2C(s) + O_2(g) \rightarrow 2CO(g)$$, $$\Delta n_g = 2 - 1 = +1$$ (increase in moles of gas). By the equation $$\frac{d(\Delta G)}{dT} = -\Delta S$$, since $$\Delta S > 0$$ (more gas moles produced), $$\Delta G$$ becomes more negative with increasing T. The slope is negative.

Reason R: The reason statement claims something about CO not decomposing at a certain temperature — this explanation is NOT correct as the reason for the negative slope. The negative slope is due to the positive entropy change, not about decomposition of CO.

The correct answer is Option (4): A is correct but R is not correct.