Question

Fermentation is represented by the equation
A) ${C_6}{H_{12}}{O_6}$$ + $$6{O_2}$$\xrightarrow{{light}}$$6C{O_2}$$ + $${H_{{2_{}}}}O$$ + $$673kcal$
B) ${C_6}{H_{12}}{O_6}$$ \to $$2{C_2}{H_5}OH$$ + $$2C{O_2}$$ + 18kcal$
C) $6C{O_2}$$ + $$12{H_2}O$$\xrightarrow{{Chlorophyll}}$${C_6}{H_{12}}{O_6}$$ + $$6{H_2}O$$ + 6{O_2}$
D) $6C{O_2}$$ + $$6{H_2}O$$ \to $${C_6}{H_{12}}{O_6}$$ + 6{O_2}$

Answer 1

Hint: Pyruvic acid formed at the end of the glycolysis can be utilised under three condition, these are
1) Lactic acid fermentation 2) Alcoholic fermentation and 3) Aerobic respiration. Former two (fermentations) occurs when there is absence of oxygen and later occurs in presence of oxygen.

Complete answer:
1) Alcoholic fermentation:
Fermentation is partial oxidation of glucose in anaerobic condition. In this set of reactions occur which convert pyruvic acid to $C{O_2}$ and ethanol in yeast.
Two enzymes, Pyruvic acid decarboxylase and alcohol dehydrogenase are involved to catalyse these reactions.
${C_6}{H_{12}}{O_6}$$ \to $$2{C_2}{H_5}OH$$ + $$2C{O_2}$$ + 18kcal$
2) Lactic acid fermentation:
 In some bacterial cells and animal muscle cells during strenuous exercise , lactic acid is formed from reduction in pyruvic acid by enzyme lactate dehydrogenase under less oxygen condition.
In both types of fermentation , reduction of pyruvic acid takes place and the reducing agent in both is $NADH + {H^ + }$which is reoxidised to $NA{D^ + }$ in both the process.

So, the correct answer is option (B).

Additional information:
In both types of fermentation ,very less amount of energy is released (less than seven percent) and rest is stored in a high bond of ATP. It is a very hazardous process as it becomes poisonous for the yeast when alcohol concentration reaches $13\% $in alcoholic fermentation.
But we have seen that alcoholic beverages obtained from this process only (yeast fermentation) contain alcoholic concentration from $40 - 50\% $. This is obtained by the process of distillation.

Note:
Above process occurs in the absence of oxygen , but if oxygen is present then aerobic respiration takes place . In this, complete oxidation of glucose occurs. First of all glucose gets converted into pyruvic acid by glycolysis (occurs in cytoplasm) and then it undergo link reaction (matrix of mitochondria) and then finally product from link reaction undergo kreb cycle (occurs in matrix of mitochondria) result in release of $C{O_2}$, water and large amount of energy.