The correct option is C 10%
Given that,
Marked price of a dinner set = ₹ 1000
Selling price of the dinner set = ₹ 900
∴ Amount of discount = ₹ (1000 - 900) = ₹ 100
Discount percent=DiscountMarked price×100
Discount percent=100×1001000=10%
Hence, he gave a discount of 10% on the dinner set.