A : Addition of HBr in buta-1, 3-diene gives 3 bromo-but-1-ene as major product at low Temperature.
R : Addition of HBr in buta-1, 3-diene gives 1-bromo-but-2-ene as major product at high temperature.

Options

A. If both Assertion & Reason are true and the reason is the correct explanation of the assertion, then mark (1).
B. If both Assertion & Reason are true but the reason is not the correct explanation of the assertion, then mark (2)
C. if Assertion is true statement but Reason is false, then mark (3)
D. If both Assertion and Reason are false statements, then mark (4)

Answer

To solve the problem, let's analyze the assertion and reason step by step.

### Step 1: Understanding the Reaction
Buta-1,3-diene is a conjugated diene, which means it has alternating double bonds. When HBr is added to buta-1,3-diene, the reaction can lead to different products depending on the conditions (temperature).

### Step 2: Low Temperature Reaction
At low temperatures, the reaction is under kinetic control. This means that the product formed is the one that is formed the fastest. The addition of HBr can occur in two ways:
- **1,2-Addition**: H adds to the first carbon, and Br adds to the second carbon, leading to the formation of 3-bromo-but-1-ene.
- **1,4-Addition**: H adds to the first carbon, and Br adds to the fourth carbon, leading to a different product.

At low temperatures, the 1,2-addition product (3-bromo-but-1-ene) is favored because it forms more quickly.

### Step 3: High Temperature Reaction
At high temperatures, the reaction is under thermodynamic control. This means that the product formed is the most stable one, even if it takes longer to form. In this case, the 1,4-addition product (1-bromo-but-2-ene) is more stable due to the more substituted double bond, which is favored at higher temperatures.

### Step 4: Conclusion
- **Assertion (A)**: True - At low temperature, 3-bromo-but-1-ene is the major product.
- **Reason (R)**: True - At high temperature, 1-bromo-but-2-ene is the major product.

However, the reason does not correctly explain the assertion because it does not address why the products differ at different temperatures.

### Final Answer
Both the assertion and the reason are true, but the reason is not the correct explanation of the assertion.