In iso-pentane, the `H` atom that can be most easily substituated by free radical mechanism is on:-
`overset(1)CH_(3)-underset(CH_(3))underset(|)overset(2)CH-overset(3)CH_(2)overset(4)CH_(3)`

Options

A. `C-1`
B. `C-2`
C. `C-3`
D. `C-4`

Explanation

To determine which hydrogen atom in iso-pentane can be most easily substituted by a free radical mechanism, we need to analyze the structure of iso-pentane and the stability of the resulting free radicals.

### Step-by-Step Solution:

1. **Identify the Structure of Iso-Pentane:**
Iso-pentane (also known as 2-methylbutane) has the following structure:
```
CH3
|
CH3-CH-CH2-CH3
```
Here, we have four carbon atoms, with the second carbon (C-2) being attached to a methyl group (CH3).

2. **Count the Types of Hydrogen Atoms:**
- **C-1 (methyl group)**: 3 hydrogen atoms (H)
- **C-2 (secondary carbon)**: 2 hydrogen atoms (H)
- **C-3 (secondary carbon)**: 2 hydrogen atoms (H)
- **C-4 (methyl group)**: 3 hydrogen atoms (H)

3. **Determine the Stability of Free Radicals:**
The stability of free radicals is crucial in determining which hydrogen can be substituted most easily. The stability order is:
- Tertiary (3°) > Secondary (2°) > Primary (1°) > Methyl (CH3)

4. **Identify the Hydrogen Leading to the Most Stable Free Radical:**
- Removing a hydrogen from C-1 or C-4 will lead to the formation of a primary free radical.
- Removing a hydrogen from C-2 will yield a tertiary free radical.
- Removing a hydrogen from C-3 will yield a secondary free radical.

5. **Conclusion:**
The hydrogen atom that can be most easily substituted by a free radical mechanism is the one on the **second carbon (C-2)**, as it leads to the formation of the most stable tertiary free radical.

### Final Answer:
The hydrogen atom that can be most easily substituted by free radical mechanism in iso-pentane is on the **second carbon (C-2)**.

---