In which of the following, oxidation state of nitrogen is lowest?

The number of moles of oxalate ions oxidised by one mole of permanganate ions in acidic medium is

If the number of moles of $\mathrm{Fe}^{2+}$ ions oxidised by one mole of acidified $\mathrm{MnO}_4^{-}$is $x$, the number of moles of $\mathrm{Fe}^{2+}$ ions oxidised by one mole of acidified $\mathrm{Cr}_2 \mathrm{O}_7^{2-}$ is

In acidic medium one mole each of $\mathrm{MnO}_4^{-}$and $\mathrm{Cr}_2 \mathrm{O}_7^{2-}$ is reduce by $x$ and $y$ moles of ferrous ions. The sum of $x$ and $y$ is