Yes, the atoms of the elements do have different masses but the same volume
B.it is not balanced for charge or for number of atoms.
It is defined as the amount of a substance that contains as many particles as there are atoms in 12 grams of pure carbon-12. So, 1 molecule contains 6.022×10^23 elementary entities of the substance.
Hope that helps
Answer : C
Because $6.65 multiplied by 4 hours equals $26.60