Which is the largest bank in India In terms of business (asked initially into the interview) and also 2nd largest.

HDFC is India’s largest private sector bank in terms of assets and market capitalization. It employs around 120,000 staff and operates a distribution network of 5,416 branches and 13,640 ATMs across 2,803 cities.
ICICI Bank is India’s second-largest bank with total assets of about Rs 112,024 crore and a network of about 450 branches and offices and about 1,750 ATMs. ICICI Bank was originally promoted in 1994 by ICICI Limited, an Indian financial institution, and was its wholly owned subsidiary.