b
\((b)\) In \(E_2\) anti-elimination take place, \(H\) and bromine must be anti to each  other \((c)\) is most favourable because both hydrogen are anti to bromine most  favourable for \(E_2\) reaction.  \((b)\) is least reactive because hydrogen and bromine both are on same side. \((b)\) is inert toward \(E_2\) reaction.