The correct answer is option 3 - Sides. The taste buds for sour taste are primarily located on the sides of the tongue.

The tongue is divided into different regions, with each region being specialized in detecting different tastes. While the front part of the tongue is generally associated with detecting sweet tastes, the sides of the tongue are responsible for sour tastes. The taste buds on the sides of the tongue contain taste receptor cells that are specifically sensitive to sour flavors.

It`s important to note that the entire tongue can still detect all tastes, but certain regions may be more sensitive to specific tastes. So, if you want to experience the full sensation of sour taste, it`s recommended to let the sour substance spread throughout your mouth.