The negative part of the addendum (the molecule to be added ) adds on to the carbon atom of the double bond containing the least number of hydrogen atoms. This rule is known as

Options

A. Saytzeff's rule
B. Peroxide rule
C. Markovnikov's rule
D. Hoffmann rule

Answer

To solve the question, we need to identify the rule that states that the negative part of the addendum (the molecule being added) attaches to the carbon atom of a double bond that has the least number of hydrogen atoms. This is a fundamental concept in organic chemistry related to the addition reactions of alkenes.

### Step-by-Step Solution:

1. **Understanding the Question**: The question describes a situation where a molecule is added to a double bond, and the negative part of this molecule attaches to the carbon atom with fewer hydrogen atoms.

2. **Identifying the Options**: The options provided are:
- a) Saytzeff rule
- b) Peroxide rule
- c) Markovnikov rule
- d) Hofmann rule

3. **Analyzing Each Option**:
- **Saytzeff Rule**: This rule pertains to elimination reactions and states that the more substituted alkene will be the major product. This does not relate to the addition of molecules to alkenes.
- **Peroxide Rule**: This rule applies to the addition of HBr in the presence of peroxides, where the negative part adds to the more substituted carbon. This is the opposite of what the question states.
- **Markovnikov Rule**: This rule states that when HX (where X is a halogen) is added to an alkene, the hydrogen atom (the positive part of the addendum) will attach to the carbon with more hydrogen atoms, while the halogen (the negative part) will attach to the carbon with fewer hydrogen atoms. This matches the description in the question.
- **Hofmann Rule**: This rule is related to elimination reactions and does not apply to the addition of molecules to alkenes.

4. **Conclusion**: Based on the analysis, the correct answer is the **Markovnikov rule**, as it directly corresponds to the statement in the question.

### Final Answer:
The rule is known as the **Markovnikov rule**.