# Heating of below one produces

$\begin{array}{1 1}(a)\;CH_2=CH_2&(b)\;CH_3CH_2CH_2-CH=CH_2\\(c)\;CH_3-CH_2-CH=CH-CH_3&(d)\;CH_3-CH_2-CH_2-CH_2-CH_3\end{array}$

This reaction is known as Hofmann elimination .In this reaction
$1^o$-hydrogen is more acidic than $2^o$-hydrogen .So the product is $CH_3CH_2CH_2-CH=CH_2$.
Hence (b) is the correct answer.