# $\Rightarrow A\overset{HBr}{\rightarrow}C_2H_5Br\overset{B}{\rightarrow}A$.A is

$\begin{array}{1 1}(a)\;C_2H_4&(b)\;C_2H_5Cl\\(c)\;C_2H_5OH&(d)\;C_2H_2\end{array}$

According to (c)
$C_2H_5OH$ and $KOH/\Delta$
$C_2H_5OH+HBr\rightarrow C_2H_5Br\overset{\overset{KOH}{\large\rightarrow}}{\Delta}C_2H_5OH+KBr$
Hence (c) is the correct answer.