The correct option is C toluene
Toluene is most readily sulfonated among these because methyl group is electron donating (+ I effect), activates benzene ring for electrophilic aromatic substitution. Because in nitrobezene and chlorobenzene, -I groups are present which deactive the ring by making the ring disfavourable for electrophilic substitution reaction. Hence, the correct answer will be option (c).