In fermentation, the incomplete oxidation of glucose is achieved under anaerobic conditions by a set of reactions where pyruvic acid is converted to $CO_2$ and ethanol. The enzymes, pyruvic acid decarboxylase and alcohol dehydrogenase, catalyse these reactions. Answer the following questions:
$(i)$ Write the chemical equation for alcoholic fermentation.
(ii) $A$ test tube containing molasses solution and yeast is kept in a warm place overnight. What gas is collected from the mixture?
(iii) How does ethyl alcohol fermentation occur?
(iv) What is pyruvic acid?

(N/A) $(i)$ The chemical equation for alcoholic fermentation is: $C_6H_{12}O_6 \rightarrow 2C_2H_5OH + 2CO_2 + \text{Energy}$.
(ii) The gas collected is $CO_2$. Yeast performs alcoholic fermentation on the sugars in molasses, producing ethanol and carbon dioxide.
(iii) Ethyl alcohol fermentation occurs in microorganisms like yeast and some bacteria under anaerobic conditions. Pyruvic acid is decarboxylated to acetaldehyde by pyruvic acid decarboxylase, and then reduced to ethanol by alcohol dehydrogenase using $NADH$.
(iv) Pyruvic acid $(CH_3COCOOH)$ is a three-carbon organic acid that serves as the end product of glycolysis in both aerobic and anaerobic respiration.