What is the number of moles in 0.025g (NH4)2Cr2O7

How would the number of moles (n) of o2 change if the atmospheric pressure doubled but all other variables stayed the same

In the millikan oil drop experiment they determined that every drop had a charge which was a while number multiple of -1.60x10^-19. if a drop has a total charge of -9.60x10^-19 then how many excess electrons are contained within the drop?

Light waves travel than sound waves.