Explanations:In English grammar, the correct use of comparative and superlative forms of adjectives is crucial for clear communication. The adjectives "far," "farther," and "farthest" are used to describe distances. "Far" is the base form, "farther" is the comparative form, and "farthest" is the superlative form.
The comparative form "farther" is used when comparing two distances. For example, if you want to say that one place is more distant from another than a third place, you would use "farther." In the given sentence, "Kolkata is farther from Delhi than Patna is," the comparative form "farther" is appropriate because it compares the distance of Kolkata from Delhi with the distance of Patna from Delhi.
On the other hand, "further" is often used in a more abstract sense or to mean "more" or "additional." For example, "We need to discuss this matter further" or "Further research is needed." However, "further" can also be used to compare physical distances, but "farther" is more commonly used and clearer in such contexts.
The base form "far" is used without comparison, such as "The city is far away." The superlative form "farthest" is used when comparing three or more distances, such as "Among the three cities, Kolkata is the farthest from Delhi."
Understanding the correct usage of these forms is essential for clear and accurate communication in English. In the context of the question, "farther" is the correct choice because it appropriately compares the distances of Kolkata and Patna from Delhi.