c
Potassium ferrocyanide is oxidised to potassium ferricyanide,

\(\mathrm{O}_{3} \rightarrow \mathrm{O}_{2}+[\mathrm{O}]\)

\(\begin{array}{l} 2 \mathrm{K}_{4}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]+\mathrm{H}_{2} \mathrm{O}+[\mathrm{O}] \rightarrow 2 \mathrm{K}_{3}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]+2 \mathrm{KOH} \\ 2 \mathrm{K}_{4}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]+\mathrm{O}_{3}+\mathrm{H}_{2} \mathrm{O} \rightarrow 2 \mathrm{K}_{3}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]+2 \mathrm{KOH}+\mathrm{O}_{2} \end{array}\)