Milk tastes sour when it is left in open for some time. This happens due to the formation of A. Lactic acid B. Citric acid C. Acetic acid D. Carbonic acid

The correct answer is A. Lactic acid.

Milk tastes sour when it is left in open for some time because of the formation of lactic acid. This is due to the action of bacteria on the lactose in milk. The bacteria convert the lactose into lactic acid, which gives milk its sour taste.

Citric acid is found in citrus fruits, such as lemons and oranges. Acetic acid is found in vinegar. Carbonic acid is found in carbonated beverages.