When a firm produces 400 units, its total cost is Rs. 6,000 and the total cost of producing 410 units is Rs. 7,500. If so, then its marginal cost will be

The correct answer is A. Rs. 1,500.

Marginal cost is the change in total cost that results from producing one additional unit of output. In this case, the marginal cost of producing the 410th unit is Rs. 1,500, because the total cost increases by Rs. 1,500 when production increases from 400 units to 410 units.

Option B is incorrect because it is the total cost of producing 410 units. Option C is incorrect because it is the change in total cost that results from producing 10 units of output. Option D is incorrect because it is not one of the possible answers.