The correct answer is: has been settled.
The verb “settle” can be used in a number of ways, but in this context it means to establish oneself in a particular place. The past participle “settled” can be used to form the present perfect tense, which is used to talk about actions that began in the past and continue to the present. In this case, the sentence is saying that Mr. John has been living in India since his wife died.
The other options are incorrect because they do not accurately reflect the meaning of the sentence. The verb “settled” cannot be used in the simple past tense (option A) because it does not express a completed action. The verb “has settled” (option C) is also incorrect because it does not express the idea that Mr. John has been living in India for a period of time. The verb “has been settling” (option D) is the only option that accurately reflects the meaning of the sentence.