c
\((c)\) This is borne out by the fact that solutions of nitric acid in pure sulphuric acid  show an almost four-fold molecular freezing-point depression (actual ly \(i \approx  3.82\)), which has been interpreted as being due to formation of the  four ions

\((1)\) \(H\ddot O\, - \,N{O_2}\,\overset {{H_2}S{O_4}} \longleftrightarrow {H_2}\mathop O\limits_ \oplus   - N{O_2}\) \(\overset {{H_2}S{O_4}} \longleftrightarrow {H_2}O{ - ^ \oplus }N{O_2}\)

\((2)\) \({H_2}O\, + \,{H_2}S{O_4}\, \rightleftharpoons \,{H_3}{O^ \oplus }\, + \,HSO_4^\Theta \)

net reaction, i.e., \(HN{O_3}\, + \,2{H_2}S{O_4}\, \rightleftharpoons \) \(^ \oplus N{O_2}\, + {H_3}{O^ \oplus } + \,2HSO_4^\Theta \)