When an object resist movement by a force

For ai it's atomic number is 13 and it's mass number is 27 how many neutrons does it have

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?

Why is carbon ideal for making different compounds?