Acid is a sour-tasting chemical substance. It is present in sour fruits like orange, sweet lime, gooseberry, etc. It is soluble in water and can neutralise alkalis or bases. It can dissolve some metals and turn blue litmus red. There are two kinds of acids: strong and weak. Hydrochloric acid, sulphuric acid, etc., are some examples of strong acids. Strong acids can corrode and result in skin burns. Weak acids corrode in a mild way and generally do not harm the skin. Many weak acids which exist naturally in foods are edible, for example, acetic acid (vinegar), citric acid (fruits), lactic acid (fermented milk products), etc.
