Explanation:

The definition of a metropolitan city can vary slightly by country and statistical agency, but a widely accepted international benchmark for a metropolitan area is a population of 1 million or more. In the Indian numbering system, 1 million is equivalent to 10 lakh. Therefore, option (1) 'more than 10 lakh' is the most appropriate general definition for the population of a metropolitan city. Options (2), (3), and (4) represent smaller urban centers or large towns, but not typically the threshold for a major metropolitan designation, which implies a significant urban agglomeration with extensive infrastructure and economic influence.