Denaturing Ethanol:
Ethanol is denatured by adding certain substances to make it unfit for human consumption. Denaturing ethanol involves adding toxic or unpleasant-tasting substances to discourage its consumption.
Substances Used to Denature Ethanol:
The following substances can be added to denature ethanol:
1. Methanol: Methanol is highly toxic and can cause blindness or even death if ingested. Adding methanol to ethanol makes it denatured and unfit for consumption.
2. Pyridine: Pyridine is a highly toxic liquid with a strong, unpleasant odor. It is often used as a denaturant to make ethanol undrinkable.
3. Copper Sulphate: Copper sulphate is a compound that is toxic and can cause various health issues if consumed. It can be added to ethanol to denature it.
Correct Answer:
The correct answer is D. All of them. All three substances - methanol, pyridine, and copper sulphate - can be added to denature ethanol.
Reasoning:
- Methanol is added to ethanol to make it unfit for consumption due to its high toxicity.
- Pyridine is used as a denaturant because of its strong odor and toxicity.
- Copper sulphate is a toxic compound that can be added to ethanol to make it unsafe for consumption.
By adding any of these substances individually or in combination, ethanol can be effectively denatured.

Denaturation is the process of adding certain substances to ethanol in order to make it unfit for consumption. This is typically done to prevent the misuse or abuse of ethanol for recreational purposes. Denatured ethanol is commonly used in industrial applications, as well as in the production of cleaning products, solvents, and fuels.

The correct answer is option 'D', which states that all of the substances mentioned (methanol, pyridine, and copper sulfate) can be added to denature ethanol. Each of these substances serves a specific purpose in the denaturation process.

1. Methanol:
Methanol, also known as wood alcohol, is a common substance used to denature ethanol. It is highly toxic and can cause blindness or even death if ingested in sufficient quantities. By adding methanol to ethanol, it renders the mixture undrinkable and dangerous for consumption.

2. Pyridine:
Pyridine is another substance that can be added to denature ethanol. It is a highly volatile liquid with a pungent odor. Pyridine is toxic and can cause irritation to the respiratory system, eyes, and skin. Similar to methanol, it makes the denatured ethanol unsuitable for consumption.

3. Copper sulfate:
Copper sulfate, also known as blue vitriol, is a compound that can be added to denature ethanol. It is a highly toxic substance that can cause irritation to the skin, eyes, and respiratory system. Copper sulfate is often used as a fungicide and herbicide. When added to ethanol, it imparts a blue color to the mixture, making it easily distinguishable from regular ethanol.

By combining these substances with ethanol, the resulting denatured ethanol becomes unfit for consumption due to the toxicity and potential health risks associated with the added substances.

In conclusion, all of the substances mentioned (methanol, pyridine, and copper sulfate) can be added to denature ethanol. Each substance serves a specific purpose in rendering ethanol undrinkable and dangerous for consumption.