Which of the following reactions involve a decrease in the length of the carbon chain:-

Options

A. Schmidt reaction
B. Hofmann's bromamide reaction
C. Hell-Volhard-Zelinski reaction
D. All of these

Answer

To determine which reactions involve a decrease in the length of the carbon chain, we will analyze each of the provided options step by step.

### Step-by-Step Solution:

1. **Analyze the First Reaction (Schemedate Reaction)**:
- The Schemedate reaction typically leads to the formation of carbonyl derivatives such as aldehydes, ketones, or carboxylic acids.
- When a carboxylic acid undergoes a reaction in acidic medium followed by treatment with azide and water, it generates a primary amine.
- In this process, the carbon chain decreases by one carbon atom as the primary amine is formed from the carboxylic acid.
- **Conclusion**: This reaction involves a decrease in the carbon chain length.

2. **Analyze the Second Reaction (Hoffman Bromamide Reaction)**:
- The Hoffman Bromamide reaction involves the conversion of a primary amide into a primary amine.
- When a primary amide reacts with bromine in the presence of potassium hydroxide, it results in the formation of a primary amine and releases carbon dioxide.
- This process also results in a decrease of one carbon atom from the original carbon chain.
- **Conclusion**: This reaction also involves a decrease in the carbon chain length.

3. **Analyze the Third Reaction (Hell-Wallet-Zelenis Reaction)**:
- The Hell-Wallet-Zelenis reaction typically involves a carboxylic acid with alpha-hydrogens reacting with chlorine in the presence of red phosphorus.
- The reaction replaces one of the alpha-hydrogens with a chlorine atom, resulting in the formation of a chloro-acetic acid.
- In this case, the carbon chain length remains the same as no carbon atoms are lost or removed.
- **Conclusion**: This reaction does not involve a decrease in the carbon chain length.

4. **Analyze the Fourth Option (All of the Above)**:
- Since the third option does not involve a decrease in the carbon chain length, the fourth option stating "all of these" is also incorrect.
- **Conclusion**: This option is wrong.

### Final Answer:
The reactions that involve a decrease in the length of the carbon chain are:
- **Option 1 (Schemedate Reaction)**
- **Option 2 (Hoffman Bromamide Reaction)**