Option 1, Geeta Chandran is a renowned Bharatanatyam dancer, not a Hindustani classical singer. She is known for her deep commitment to the classical art form.

Option 2, Leela Samson is also a celebrated personality, but her domain is dance, not singing. She is a Bharatanatyam dancer, instructor, and choreographer.

Option 3, Gangubhai Hangal, is indeed the correct answer. She was a revered exponent of the Kirana gharana tradition in Hindustani classical music, and her specialty was Khayal, a form of vocal performance in Indian classical music.

Option 4, Swapnasundari, is chiefly recognized for her contributions to the world of dance. She is both a Bharatanatyam and Kuchipudi dancer and not associated with Hindustani classical singing.

So, the correct answer is indeed Gangubhai Hangal, who was a legendary performer in Hindustani classical music.