Identify A and B in the following reactions:

Question

 

 

$$\begin {array} {1 1} (a)\;A=C_2H_2,B=C_2H_6 & \quad (b)\;A=C_2H_5Cl,B=C_2H_4 \\ (c)\;A=C_2H_4,B=C_2H_5Cl & \quad (d)\;A=C_2H_5Cl,B=C_2H_5Cl \end {array}$$