A : When isobutane-is-reacted with `Cl_(2)` in presence of sunlight then `CH_(3)-overset(CH_(3))overset(|)CH-CH_(3)Cl` is formed in high percentage.
R : The reactivity of `1^(@), 2^(@) “and” 3^(@)` H-atoms towards chlorine are 1 : 3.8 : 5 respectively.

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 assertion-reason question regarding the reaction of isobutane with chlorine in the presence of sunlight, we will analyze both the assertion (A) and the reason (R) step by step.

### Step 1: Analyze the Assertion (A)
The assertion states that when isobutane reacts with Cl₂ in the presence of sunlight, the product formed is `CH₃-CH(CH₃)-CH₂Cl` in high percentage.

**Explanation:**
- Isobutane (C₄H₁₀) has the structure:
```
CH₃
|
CH₃-CH-CH₂
```
- When isobutane reacts with Cl₂ under UV light, it undergoes free radical halogenation.
- The chlorine (Cl₂) breaks down into chlorine radicals (Cl·) due to the energy from sunlight.
- The reaction can lead to the substitution of hydrogen atoms by chlorine atoms.

### Step 2: Identify the Product
The product mentioned, `CH₃-CH(CH₃)-CH₂Cl`, indicates that a chlorine atom has replaced one of the hydrogen atoms on the second carbon (the one with the methyl group).

### Step 3: Analyze the Reason (R)
The reason states that the reactivity of 1°, 2°, and 3° hydrogen atoms towards chlorine are in the ratio of 1:3.8:5 respectively.

**Explanation:**
- In isobutane, there are:
- 9 hydrogen atoms in total.
- 5 of these are tertiary (3°) hydrogen atoms, which are more reactive.
- 3 are secondary (2°) hydrogen atoms, which have moderate reactivity.
- 1 is primary (1°) hydrogen atom, which is the least reactive.
- The reactivity ratios indicate that 3° hydrogen atoms are most likely to be replaced by chlorine due to their higher reactivity.

### Step 4: Conclusion
- The assertion is true because the product `CH₃-CH(CH₃)-CH₂Cl` is indeed formed in high percentage when isobutane reacts with Cl₂.
- The reason is also true as it correctly describes the reactivity of hydrogen atoms.
- However, the reason does not correctly explain the assertion. The major product is formed not just because of the reactivity ratios, but also due to the number of replaceable hydrogen atoms.

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