44 given the balanced ionic equation:
3pb2+ + 2cr ==> 3pb + 2cr3+
what is the number of moles of electrons gained by 3.0 moles of lead ions?
(1) 5.0 mol (3) 3.0 mol
(2) 2.0 mol (4) 6.0mol
i know that the answer is 4 i just need an explanation of how

The content of manganese (mn) in steel was determined spectrophotometrically and with the use of the standard addition method. an unknown sample of mn from a digested steel sample gave an absorbance of 0.185 when analyzed spectrophotometrically. when 5.00 ml of solution containing 95.5 ppm mn was added to 50.0 ml of the unknown steel solution (digested sample), the absorbance was 0.248. calculate the concentration, in parts-per-million (ppm), of mn in the digested steel sample solution.