India is a peculiar country and there are a variety and various languages spoken in the Indian sub-contenent.
Hindi is commonly used in North Indian states, while Telugu, Tamil, Kannada and Malayalam are spoken in south India.
Hindi was declared as one of the official languages, because it is spoken by most number of people in India. Almost every north-Indian knows Hindi.
English is another official language, extensively used in South Indian states, especially Tamil Nadu and Andhra Pradesh and other metropolitan cities in the rest of India.