Butter contains [[1]] acid.

A substance is said to be an acid if it tastes sour and turns blue litmus red. When it interacts with a base, salt and water are produced. Both powerful and weak acids exist. Butter includes four carbon atoms in its acid.

The acids may be divided into many groups and can be both inorganic and inorganic acids. Organic acids are those that are frequently found in nature. They include tartaric acid, which is present in tamarind, formic acid, which is frequently present in ant bites, maleic acid, which is present in apples, lactic acid, which is present in milk, ascorbic acid, which is present in lemons, etc.

The acid that is commonly found in rancid or stable butter is called “butyric acid”.

In addition to these inorganic, or weak, acids present in nature, sulphuric, nitric, and phosphoric acids, to name a few, are examples of powerful inorganic acids that are created from naturally existing minerals. These acids have a corrosive character and are quite severe. They may react with certain metals, which causes them to release hydrogen gas thereafter. These acids are frequently employed as the starting ingredients in the synthesis of many compounds.

Hence, the answer is butyric acid.