b
\(\begin{array}{*{20}{c}}
  {\begin{array}{*{20}{c}}
  {\,\,Br\,\,\,\,\,\,} \\ 
  | \,\,\,\,\,
\end{array}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,} \\ 
  {\mathop {{H_3}C}\limits^{({1^o})}  - \mathop {CH}\limits_{({2^o})}  - \mathop {CH}\limits^{({2^o})}  - \mathop {C{H_3}}\limits^{({1^o})} } \\ 
  {\,\,\,\,\,\,\,\,\,\,\,\,\,|} \\ 
  {\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,Br} 
\end{array}\)

\(2\) secondary carbon present and \(2\) secondary hydrogen present.