Step 1: Identify the substrate:
The starting compound is 2-chlorobutane, $\text{CH}_3\text{CHClCH}_2\text{CH}_3$.
Step 2: Form A:
Mg in dry ether gives $\text{R-MgCl}$ with $\text{R} = $ sec-butyl.
Step 3: Protonolysis:
Ethanol supplies $\text{H}^+$. The R group of the Grignard reagent picks up this hydrogen to become R-H, and the magnesium ends up as magnesium ethoxide chloride.
Step 4: Name the product:
R-H with R = sec-butyl is $\text{CH}_3\text{CH}_2\text{CH}_2\text{CH}_3$, butane. This is the zigzag four-carbon figure in option (B).
Final Answer:
The product B is butane, option (B).
\[ \boxed{\text{Butane (B)}} \]
