You all know that lemon, tomato, oranges tastes sour. You also know that all of them contains citric acid. This is the best natural example to prove that acids are sour in taste.
On the other hand you all know that increased amount of baking soda makes the cake taste bitter. This is because baking soda is a base and hence tastes bitter.
When tested on a litmus paper acids turn the colour of the litmus to red whereas bases turns the colour of the litmus to blue.
Fig. lemon (acidic) and baking soda (basic)