(B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A). Metals high in the reactivity series are extracted by electrolytic reduction, not displacement.
The Assertion is true — highly reactive metals (Na, Mg, Al, Ca, K) cannot be reduced by carbon because they have more affinity for oxygen than carbon. The Reason is also true — displacement reactions (e.g., thermite reaction) are used to obtain metals. However, displacement reactions explain how mid-series metals are extracted, not why top-series metals cannot be reduced by carbon. So R does not explain A → option (B).