Maximum number of molecules of \(\mathrm{CH}_{3} \mathrm{I}\) that can react with a molecule of \(\mathrm{CH}_{3} \mathrm{NH}_{2}\) are

\(\mathrm{CH}_{3} \mathrm{NH}_{2} \underset{\substack{\text { Methly } \\ \text { amine }}}{\stackrel{\mathrm{CH}_{3} \mathrm{I}}{\longrightarrow}} \underset{-\mathrm{HI}}{\longrightarrow}\left(\mathrm{CH}_{3}\right)_{2} \mathrm{NHH} \underset{\begin{array}{c}\text { Dimethyl } \\ \text { amine }\end{array}}{\stackrel{\mathrm{CH}{ }_{3} \mathrm{I}}{\longrightarrow}} \underset{-\mathrm{HI}}{\longrightarrow}\)
\(\left(\mathrm{CH}_{3}\right)_{3} \mathrm{~N}\) Trimethyl amine \(\downarrow \mathrm{CH}_{3} \mathrm{I}\)
\(\left(\mathrm{CH}_{3}\right)_{4} \mathrm{~N}^{+} \mathrm{I}^{-}\)
Tetramethyl ammonium iodide
Hence, three molecules of \(\mathrm{CH}_{3} \mathrm{I}\) is used.