Glucose fermentation by yeast yields.
(a) Ethanol + ${CO_2}$
(b) Ethanol+${H_2O}$
(c) Methanol +${CO_2}$
(d) ${H_2O}$+${CO_2}$

Hint: Fermentation is an anaerobic process that takes place without the use of molecular oxygen. It is also called alcoholic Fermentation because in this production alcohol takes place and it is also involved in lactic acid Fermentation.

Complete answer:
In the fermentation of glucose, the first pyruvate undergoes decarboxylation with the removal of the carboxyl group in the form of carbon dioxide. This reaction takes place with the help of the enzyme pyruvate decarboxylase transacetylase which leads to the production of acetaldehyde and carbon dioxide. Acetaldehyde after hydrogenation gets reduced to ethyl alcohol with the help of enzyme alcohol dehydrogenase.

Additional Information:
Lactic acid Fermentation takes place by lactic acid bacteria and muscles in which pyruvic acid from glycolysis get reduced to form lactic acid. The reaction takes place by an enzyme lactic dehydrogenase which requires Flavin mononucleotide and zinc ion. In muscles accumulation of lactic acid leads to muscular fatigue and at rest lactic acid gets re-convert to pyruvic acid and then entered into the aerobic respiration process.
The energy-yielding in aerobic respiration is more than anaerobic because of the incomplete breakdown of the respiratory substrate, the organic end product still contains energy and re-utilisation of by-products placed in anaerobic reaction. In anaerobic reactions, oxygen is not used for accepting the electron and protons.

So, the correct answer is 'Ethanol + ${CO_2}$'.

Note:
The fermentation process was discovered by Louis Pasteur in 1857, but its successful experimentation by use of sugar solution with yeast extract was done by Eduard Buchner in 1897. This proved that Fermentation takes place by yeast extract instead of living yeast cells.