According to Indian Census, urban towns and cities are grouped into how many of the following classes?

Six

The correct answer is Option (4) → Six

Census of India classifies urban centres into six classes.  Urban centre with population of more than one lakh is called a city or class I town. Cities accommodating population size between one to five million are called metropolitan cities an more than five million are mega cities. Majority of metropolitan and mega cities are urban agglomerations.