Anaerobic respiration involves the incomplete breakdown of glucose. it releases around 5percentage of the energy released by aerobic respiration. in yeast it can be observed, as alcoholic fermentation. option 'C'.

**Explanation:**

In anaerobic respiration, the breakdown of sugars occurs in the absence of oxygen. This process is also known as fermentation. The incomplete breakdown of sugars in anaerobic respiration leads to the formation of alcohol (such as ethanol) and carbon dioxide (CO2). This process is commonly observed in yeast, bacteria, and some other microorganisms.

**The breakdown of glucose in anaerobic respiration can be summarized as follows:**

1. **Glycolysis:** The initial step in anaerobic respiration is glycolysis, which occurs in the cytoplasm of the cell. During glycolysis, one molecule of glucose is converted into two molecules of pyruvate. This process produces a small amount of ATP (adenosine triphosphate) and NADH (nicotinamide adenine dinucleotide).

2. **Conversion of pyruvate to ethanol:** In the absence of oxygen, pyruvate is converted into ethanol through a process called alcoholic fermentation. This step involves the conversion of pyruvate to acetaldehyde by the enzyme pyruvate decarboxylase. Acetaldehyde is then converted into ethanol by the enzyme alcohol dehydrogenase. This reaction regenerates NAD+ from NADH, allowing glycolysis to continue.

3. **Release of carbon dioxide:** During alcoholic fermentation, carbon dioxide is released as a byproduct. This is why the process is often used in baking and brewing, as the carbon dioxide produced contributes to the rising of dough or the formation of bubbles in alcoholic beverages.

4. **Overall equation:** The overall equation for anaerobic respiration in yeast can be represented as:
Glucose → 2 ethanol + 2 carbon dioxide + 2 ATP

Therefore, the correct answer is option 'C' - Alcohol and CO2 are formed during the incomplete breakdown of sugars in anaerobic respiration.