The oxidation state of nitrogen in compound
So, you know that one mole of hydrazine,
The oxidation state of hydrogen in hydrazine is +1, which means that, in order for the compound to be neutral, the oxidation state of nitrogen must be
A very important pirce of information given to you is the fact that the oxidation state of hydrogen remains unchanged. Since 1 mole of hydrazine contains 2 moles of nitrogen, this means that the 10 moles of electrons will come from the 2 moles of nitrogen.
As a result, each nitrogen atom will lose 5 electrons.
If each nitrogen atom loses 5 electrons, its oxidation state will go from -2 to +3