Which one of the following is not a buffer solution?

Options

1. A$0.8 \mathrm{M} \mathrm{H}_2 \mathrm{~S}+0.8 \mathrm{M} \mathrm{KHS}$
2. B$2 \mathrm{M} \mathrm{C}_6 \mathrm{H}_5 \mathrm{NH}_2+2 \mathrm{M} \mathrm{C}_6 \mathrm{H}_5 \mathrm{NH}_3{ }^{+} \mathrm{Br}^{-}$
3. C$3 \mathrm{M} \mathrm{H}_2 \mathrm{CO}_3+3 \mathrm{M} \mathrm{KHCO}$
4. D$0.05 \mathrm{M} \mathrm{KClO}_4+0.05 \mathrm{M} \mathrm{HClO}_4$