What is the sum of 0.04321 g + 5.263 g + 2.13 g to the correct number of significant digits

Iknow #2 is d. i just need to know why

When you perform this reaction, what could remain at the end of the reaction? check all that apply. excess reactant aqueous copper chloride excess reactant aluminum oxygen product solid copper carbon dioxide product aqueous aluminum chloride water

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?