1-butene when treated with HBr gives:

Options

A. sec-butyl bromide
B. n-butyl bromide
C. 1-bromo butane
D. 3-butyl bromide

Explanation

To solve the question of what product is formed when 1-butene is treated with HBr, we can follow these steps:

### Step 1: Understand the Reactants
1-butene is an alkene with the following structure:
```
CH2=CH-CH2-CH3
```
This means that there is a double bond between the first and second carbon atoms.

### Step 2: Identify the Reaction
When 1-butene reacts with HBr (hydrobromic acid), it undergoes an electrophilic addition reaction. In this reaction, the double bond will react with HBr.

### Step 3: Apply Markovnikov's Rule
According to Markovnikov's rule, when HX (where X is a halogen) adds to an alkene, the hydrogen atom will attach to the carbon atom that has the greater number of hydrogen atoms already attached.

In 1-butene:
- The first carbon (C1) has 2 hydrogen atoms.
- The second carbon (C2) has 1 hydrogen atom.

Thus, the hydrogen from HBr will attach to C1 (the carbon with more hydrogen atoms).

### Step 4: Formation of Carbocation
After the addition of H+, a carbocation is formed. In this case, the carbocation will be formed on C2, which is a secondary carbocation (since it is attached to two other carbon atoms).

### Step 5: Nucleophilic Attack by Bromide Ion
The bromide ion (Br-) will then attack the positively charged carbon (C2), leading to the formation of the product.

### Step 6: Write the Final Product
The product formed will be:
```
CH3-CHBr-CH2-CH3
```
This compound is known as secondary butyl bromide.

### Conclusion
When 1-butene is treated with HBr, the product formed is secondary butyl bromide.