$$2 \mathrm{MnO}_4^{-}+\mathrm{bI}^{-}+\mathrm{cH}_2 \mathrm{O} \rightarrow x \mathrm{I}_2+y \mathrm{MnO}_2+z \overline{\mathrm{O}} \mathrm{H}$$

If the above equation is balanced with integer coefficients, the value of $$z$$ is ________.

The oxidation number of iron in the compound formed during brown ring test for NO$$_3^-$$ iron is ________.

See the following chemical reaction:

$$\mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}+\mathrm{XH}^{+}+6 \mathrm{~F}_{e}^{2+} \rightarrow \mathrm{YCr}^{3+}+6 \mathrm{~F}_{e}^{3+}+\mathrm{Z} \mathrm{H}_{2} \mathrm{O}$$

The sum of $$\mathrm{X}, \mathrm{Y}$$ and $$\mathrm{Z}$$ is ___________

In alkaline medium, the reduction of permanganate anion involves a gain of __________ electrons.