Photochemical chlorination of alkane is initiated by a process

• Following the cleavage of the link, the two electrons in Cl-Cl bonds are distributed equally between the two chlorine atoms. 
• Homolysis is the process where by the two electrons in a bond are distributed equally amongst the two bonding atoms after the link has been broken. Therefore, homolysis is the catalyst that starts the photochemical chlorination of an alkane. 

Hence, the correct answer (C). Homolysis.