Which of the following reactions follows Markovnikov's rule?

Options

A. `C_2H_4+HBr`
B. `C_3H_6+Cl_2`
C. `C_3H_6+HBr`
D. `C_3H_6+Br_2`

Explanation

To determine which of the given reactions follows Markovnikov's rule, we will analyze each reaction step by step.

### Step-by-Step Solution:

1. **Identify the Reactions**:
We have four reactions to analyze:
- Reaction 1: C2H4 + HBr
- Reaction 2: C3H6 + Cl2
- Reaction 3: C3H6 + HBr
- Reaction 4: C3H6 + Br2

2. **Analyze Reaction 1: C2H4 + HBr**:
- C2H4 is ethylene (CH2=CH2).
- When HBr adds to ethylene, according to Markovnikov's rule, the hydrogen (H) will add to the carbon with more hydrogen atoms (which is both in this case).
- Since both carbons have the same number of hydrogen atoms, this reaction does not favor Markovnikov's rule.
- **Conclusion**: Reaction 1 does not follow Markovnikov's rule.

3. **Analyze Reaction 2: C3H6 + Cl2**:
- C3H6 is propene (CH3-CH=CH2).
- The addition of Cl2 will result in a halogenation reaction, forming a vicinal dihalide (both Cl atoms will add to the double bond).
- This reaction does not involve the addition of H and Cl in a manner that follows Markovnikov's rule.
- **Conclusion**: Reaction 2 does not follow Markovnikov's rule.

4. **Analyze Reaction 3: C3H6 + HBr**:
- Again, C3H6 is propene (CH3-CH=CH2).
- According to Markovnikov's rule, the hydrogen (H) will add to the carbon with more hydrogen atoms (the CH2 end), and the bromine (Br) will add to the carbon with fewer hydrogen atoms (the CH end).
- The product will be CH3-CHBr-CH3.
- **Conclusion**: Reaction 3 follows Markovnikov's rule.

5. **Analyze Reaction 4: C3H6 + Br2**:
- This reaction involves the addition of bromine to propene.
- Similar to Reaction 2, this will lead to the formation of a vicinal dibromide without following Markovnikov's rule.
- **Conclusion**: Reaction 4 does not follow Markovnikov's rule.

### Final Answer:
The reaction that follows Markovnikov's rule is **Reaction 3: C3H6 + HBr**.