The incorrect statement among the following is:
\( \mathrm{NO_2} \) can dimerise easily
\( \mathrm{PF_3} \) exists but \( \mathrm{NF_5} \) does not.
\( \mathrm{SO_2} \) can act as an oxidizing agent, but not as a reducing agent
\( \mathrm{PH_3} \) shows lower proton affinity than \( \mathrm{NH_3} \).