During the alcoholic fermentation of sugar by yeast, which organic compound is always formed as the main alcohol end product along with carbon dioxide?

Introduction / Context:
Fermentation is an anaerobic process carried out by microorganisms such as yeast. This question focuses on the specific alcohol produced when yeast ferments sugars during brewing and baking. Understanding that yeast converts sugars into ethyl alcohol and carbon dioxide is central to microbiology, food science and industrial biotechnology.

Given Data / Assumptions:
- Yeast can ferment sugars like glucose under anaerobic conditions.- The options list methyl alcohol, ethyl alcohol, acetic acid, ethylene and lactic acid.- The question asks which compound is always formed as the main alcohol end product in this fermentation.- We assume the context of typical yeast fermentation used in bread making and alcoholic beverages.

Concept / Approach:
During alcoholic fermentation, yeast enzymes convert glucose into ethanol and carbon dioxide. The overall simplified reaction is glucose yielding two molecules of ethanol plus two molecules of carbon dioxide and energy. Ethyl alcohol, also known as ethanol, is the alcohol found in beer, wine and spirits, and carbon dioxide produced helps bread dough rise. Methyl alcohol is more toxic and is not produced by normal yeast fermentation. Acetic acid is formed by acetic acid bacteria, not by yeast in standard brewing. Ethylene is a plant hormone gas, and lactic acid is produced in lactic acid fermentation by certain bacteria and muscle cells. Therefore, the correct answer is ethyl alcohol or ethanol.

Step-by-Step Solution:
Step 1: Recall that the primary products of yeast fermentation of sugar are ethanol and carbon dioxide.Step 2: Recognise that ethanol is the same as ethyl alcohol, commonly associated with alcoholic drinks.Step 3: Note that the question asks specifically for the alcohol end product, not the gas.Step 4: Identify ethyl alcohol also called ethanol in option B and verify that it matches the known end product.Step 5: Select option B as the correct answer.

Verification / Alternative check:
Biochemistry sources describe alcoholic fermentation as conversion of pyruvate to ethanol and carbon dioxide via intermediate acetaldehyde.Industrial descriptions of breweries and distilleries emphasise ethanol production by yeast, confirming that ethyl alcohol is the final product.No standard fermentation process using yeast lists methanol, acetic acid, ethylene or lactic acid as the main alcohol product, which supports the choice.

Why Other Options Are Wrong:
Option A is wrong because methyl alcohol or methanol is not normally produced in significant amounts by yeast and is highly toxic to humans.Option C is wrong because acetic acid is produced when ethanol is further oxidised by acetic acid bacteria, not during primary alcoholic fermentation by yeast.Option D is wrong because ethylene is a gaseous hydrocarbon plant hormone used in artificial ripening, not a product of yeast sugar fermentation.Option E is wrong because lactic acid is produced in lactic acid fermentation carried out by certain bacteria and in oxygen debt conditions in muscles, not in alcoholic fermentation by yeast.

Common Pitfalls:
Students sometimes mix up different fermentation pathways and think that lactic acid or acetic acid might be produced by yeast under all conditions.Another pitfall is to confuse ethanol with methanol because both are alcohols, but their production pathways and safety profiles differ greatly.Remember that when you see yeast fermenting sugar in brewing or baking, the characteristic alcohol produced is ethyl alcohol or ethanol.

Final Answer:
During fermentation of sugar by yeast, the compound that is always formed as the main alcohol end product is ethyl alcohol, also called ethanol.