`H_(3)C-underset(CH_(3))underset(|)C=CH_(2)+HBr to A`
A (predominantly) is:

Options

A. `CH_(3)-underset(CH_(3))underset(|)overset(Br)overset(|)C-CH_(2)CH_(3)`
B. `CH_(3)-underset(Br)underset(|)CH-underset(CH_(3))underset(|)CH-CH_(3)`
C. `CH_(3)-underset(CH_(3))underset(|)CH-underset(Br)underset(|)CH-CH_(3)`
D. `CH_(3)-underset(CH_(3))underset(|)CH-CH_(2)-CH_(2)Br`

Explanation

To solve the problem, we need to analyze the reaction of the given compound with HBr and determine the major product formed. The compound is 2-methylpropene (H3C-CH(CH3)=CH2), and it reacts with HBr.

### Step-by-Step Solution:

1. **Identify the Reactants:**
The reactant is 2-methylpropene (H3C-CH(CH3)=CH2) and it reacts with HBr.

2. **Understand the Reaction Mechanism:**
HBr dissociates into H⁺ and Br⁻. The H⁺ ion will attack the double bond (C=C) of 2-methylpropene.

3. **Formation of Carbocations:**
When H⁺ adds to the double bond, two possible carbocations can form:
- **Carbocation 1:** If H⁺ adds to the terminal carbon (C1), we get a secondary carbocation at C2 (CH3-CH⁺-CH2-CH3).
- **Carbocation 2:** If H⁺ adds to the middle carbon (C2), we get a more stable tertiary carbocation at C1 (CH3-CH2-CH⁺-CH3).

4. **Stability of Carbocations:**
The stability of carbocations increases with the number of alkyl groups attached. Tertiary carbocations are more stable than secondary ones.
- Carbocation 1 (secondary) has 1 alkyl group.
- Carbocation 2 (tertiary) has 3 alkyl groups.

5. **Select the More Stable Carbocation:**
The tertiary carbocation is more stable due to hyperconjugation and inductive effects from the three methyl groups. Therefore, the reaction will proceed through this carbocation.

6. **Nucleophilic Attack by Br⁻:**
After the formation of the more stable tertiary carbocation, the Br⁻ ion will attack this positively charged carbon, leading to the formation of the product.

7. **Final Product:**
The major product formed from this reaction is 2-bromo-2-methylpropane (CH3-C(CH3)(Br)-CH3).

### Conclusion:
The predominantly formed product A is 2-bromo-2-methylpropane.