a
\(\underset{\underset{Acts\,as\,base}{\mathop{\downarrow }}\,}{\mathop{HO\,-\,\,N{{O}_{2}}}}\,\,+\,\,\underset{\underset{Act\,as\,Acid}{\mathop{\downarrow }}\,}{\mathop{H\,-\,OS{{O}_{3}}H}}\,\,\,\to \,\) \(\,\overset{+}{\mathop{N}}\,{{O}_{2}}\,+\,\,{{H}_{2}}O\,\,+\,\,\overset{-}{\mathop{H}}\,S{{O}_{4}}\)