Correct Answer:

Sides

Solution : The correct option is sides.

The sides of the tongue contains the cells responsible for sour taste. This is due to the location of the sour taste buds on the side of the tongue, near the soft palate. Acids trigger the sour taste receptors. When one consume anything sour, the acids connect to taste receptors and send a signal to the brain, alerting  to the fact that the food is sour. The sweet receptors are in the front of the tongue, salty at the tip of the tongue, bitter at the back of the tongue, umami at the front and back of the tongue.