This looks like Redox chemistry:
Fe(0) goes to Fe(3+) & N(+5) goes to N(+2), so 3 electrons xfr'd
This is a combustion reaction...electrons are not actually transfered; they are treated as though they were transfered for purposes of balancing oxidation states....in that case you can say:
O2 (0) goes to two O(2-), so 4 electrons, but 7 O2 react and each one xfrs 4 electrons, so 4 x 7 electrons, or 28 electrons xfr'd here.
Ag(+) goes to Ag(0) & Br(-) goes to Br(0), so 1 electrosn xfr'd, but it happens for each AgBr molecule and two molecules react, so 1 x 2, or just 2 electrons xfr'd here.
