How many β-carbon atoms does 2-Bromobutane have?

The correct answer is option 3 --  2.

Structure of 2-bromobutane: CH₃–CH(Br)–CH₂–CH₃

• The carbon attached to Br is the α-carbon.
• The carbons directly adjacent to the α-carbon are called β-carbons.

Here, the α-carbon is the second carbon.
Adjacent to it are:

• C₁ (CH₃ on the left)
• C₃ (CH₂ on the right)

So, there are 2 β-carbons.