The number of electrons involved in the reduction of nitrate ion to hydrazine is:
8
5
3
7
NO−3→N2H4
Oxidation state of N in NO−3 is +5. Oxidation state of N in N2H4 is -2.
So, the number of electrons involved are 7.
The number of electrons involved in the reduction of Cr2O2−7 in acidic solution to Cr3+ is