The product formed in the first step of the reaction of
`CH_(3)-CH_(2)-overset(Br)overset(|)CH-CH_2-underset(Br)underset(|)CH-CH_3` with excess
`Mg//Et_(2)O(Et = C_2H_5)` is :

Options

A. `{:(CH_(3)-CH_(2)-CH-CH_2-CH-CH_3),(" "|" "|),(" "CH_3-CH-CH_2-CH-CH_2-CH_3):}`
B. `{:(CH_3-CH_2-CH-CH_2-CH-CH_3),(" "|" "|),(CH_3-CH_2-CH-CH_2-CH-CH_3):}`
C.
D. `CH_3CH_2- overset(MgBr)overset(|)CH-CH_2-underset(MgBr)underset(|)CH-CH_3`

Answer

To solve the problem, we need to identify the product formed in the first step of the reaction of 2,4-dibromohexane with excess magnesium in diethyl ether.

### Step-by-Step Solution:

1. **Identify the starting material**: The compound given is 2,4-dibromohexane. This can be represented as:
\[ \text{CH}_3-\text{CH}_2-\text{Br}-\text{CH}-\text{Br}-\text{CH}_2-\text{CH}_3 \]
where the bromine atoms are located at the 2nd and 4th carbon positions.

2. **Understand the reaction conditions**: The reaction is performed with excess magnesium (Mg) in diethyl ether (Et2O). This is a typical setup for a Wurtz reaction, which is used to couple alkyl halides.

3. **Mechanism of the reaction**: In the presence of magnesium, the bromine atoms will react with magnesium to form a Grignard reagent. The magnesium inserts itself between the carbon and bromine atoms, leading to the formation of:
\[ \text{CH}_3-\text{CH}_2-\text{CH}-\text{CH}_2-\text{CH}_2-\text{CH}_3 \]
and magnesium bromide (MgBr2) as a byproduct.

4. **Write the product**: The product formed after the first step, where magnesium inserts itself, will be:
\[ \text{CH}_3-\text{CH}_2-\text{C}(\text{MgBr})-\text{C}(\text{MgBr})-\text{CH}_2-\text{CH}_3 \]
This indicates that the bromine atoms have been replaced by magnesium bromide groups.

5. **Final product representation**: The final product can be represented as:
\[ \text{CH}_3-\text{CH}_2-\text{C}(\text{MgBr})-\text{C}(\text{MgBr})-\text{CH}_2-\text{CH}_3 \]

### Conclusion:
The product formed in the first step of the reaction is:
\[ \text{CH}_3-\text{CH}_2-\text{C}(\text{MgBr})-\text{C}(\text{MgBr})-\text{CH}_2-\text{CH}_3 \]