Which one of the following belongs to the domain of positive degree sentence?

Positive degree is the base/plain form of an adjective or adverb with no comparison involved. It simply describes a quality without comparing it to anything.

"Kashmir is the most beautiful place in the world" is a Superlative Degree sentence, not a positive degree, because of the word "most beautiful."

Similarly, lead is the heaviest of all metals, is superlative, and Marina is fatter than Clara is comparative. Hence, Kalidasa was a great poet in ancient India, which is the only positive degree sentence among the options.