Among the following organic acids, the acid present in rancid butter is:

The question asks which organic acid is present in rancid butter among the given options.

Rancid butter develops an unpleasant odor due to the breakdown of fats. This process releases short-chain fatty acids. Specifically, butyric acid is known to be responsible for the characteristic smell of rancid butter.

Now, let's examine each option:

Option A: Pyruvic acid has the formula $$CH_3COCOOH$$. It is an intermediate in metabolic pathways and is not associated with rancid butter.

Option B: Acetic acid has the formula $$CH_3COOH$$. It is the main component of vinegar and gives vinegar its sour taste, but it is not the acid in rancid butter.

Option C: Butyric acid has the formula $$CH_3CH_2CH_2COOH$$. It is a short-chain fatty acid produced when butter becomes rancid due to the hydrolysis of triglycerides, leading to the release of butyric acid, which causes the foul smell.

Option D: Lactic acid has the formula $$CH_3CH(OH)COOH$$. It is found in sour milk and is produced during anaerobic respiration in muscles, but it is not the acid in rancid butter.

Therefore, butyric acid is the acid present in rancid butter.

Hence, the correct answer is Option C.