The correct answer for the question "Who among the following taught the doctrine of `Shunyata`?" is option 1: Nagarjuna.

Nagarjuna was an influential Indian philosopher and Buddhist monk who lived in the 2nd century CE. He is recognized as the founder of the Madhyamaka school of Mahayana Buddhism. The doctrine of `Shunyata` or `Emptiness` is a fundamental concept in Madhyamaka philosophy.

Option 2: Shankaracharya, also known as Adi Shankara, was an influential figure in the Advaita Vedanta philosophy of Hinduism. While Shankaracharya discusses the concept of `Maya` (illusion), he does not specifically teach the doctrine of `Shunyata`.

Option 3: Harisena was an ancient Indian poet in the court of Emperor Harsha. There is no evidence to suggest that he taught the doctrine of `Shunyata`.

Option 4: Vallabhacharya was a 16th-century philosopher and theologian who founded the Pushtimarg sect in Hinduism. He focused on the devotion and worship of Lord Krishna and did not teach the doctrine of `Shunyata`.

Therefore, the