The correct answer is option 3, Indo-Aryan.
Option 1, Sino-Tibetan, is a language family that includes languages spoken in China, Tibet, and parts of Southeast Asia. While there are some Sino-Tibetan languages spoken in India, they are not the largest linguistic group.
Option 2, Austric, is a proposed language family that includes the Austroasiatic and Austronesian language families. While there are some Austroasiatic languages spoken in India, they are not the largest linguistic group.
Option 4, Dravidian, is a language family that includes languages spoken predominantly in South India and some regions of Sri Lanka. It is the fourth largest linguistic group in India, but not the largest.
Option 3, Indo-Aryan, refers to the branch of the Indo-European language family that includes languages such as Hindi, Bengali, Punjabi, and Gujarati. Indo-Aryan languages are spoken by the majority of the population in North India and parts of Central and East India, making it the largest linguistic group in India.