Correct Answer - C
Electron releasing groups such a `-CH_3, -OCH_3` activate the monomer towards cationic polymerisation because these groups provide stability to the carbocation formed. On the other hand, `-NO_2` is a electron withdrawing group.So, it reduces the stability of carbocation formed. Thus , the correct order is `underset"(III)"(CH_2=CH-C_6H_4(OCH_3)) gt underset"(II)"(CH_2=CH-C_6H_4(CH_3)) gt underset"(I)"(CH_2=CH-C_6H_4(NO_2))`