$C{H_3} - C{H_2} - C{H_2} - C{H_3}\xrightarrow[{475\,K}]{{{H_2}S{O_4}}} $$\mathop {C{H_2} = CH - C{H_2} - C{H_3}}\limits_{{\text{Less}}{\mkern 1mu} {\text{symmetrical}}{\mkern 1mu} {\text{or}}{\mkern 1mu} {\text{unsymmetrical}}{\mkern 1mu} ({\text{minor}}{\mkern 1mu} {\text{product}})} $
It is based on Saytzeff's rule. According to this more symmetrical or more alkylated alkene predominates.
$\begin{array}{*{20}{c}}
{C{H_3}C{H_2}CH - C{H_2}} \\
{\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,|\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,|} \\
{\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,Br\,\,\,\,\,\,\,\,\,Br\,\,}
\end{array}\xrightarrow[\begin{subarray}{l}
(ii)\,NaN{H_2} \\
in\,liq.\,N{H_3}
\end{subarray} ]{{(i)\,KOH\,alc.}}$