Can anyone explain how to use an activity series in chemistry? My teacher doesn't explain thoroughly.

Part of molten rock at mid-ocean ridges

Which formula can be used to calculate the molar mass of hydrogen peroxide

For the reaction shown, calculate how many moles of no2 form when each of the following completely reacts. 2n2o5(g)→4no2(g)+o2(g) part a 1.0 mol n2o5 express your answer using two significant figures. nothing mol m o l request answer part b 5.4 mol n2o5 express your answer using two significant figures.