What is the mass in grams of 1.9×1023 atoms of lead?

Explanation:

# moles that exist in 1.9 X 10 23 =

             =  # of atoms/# of Avogadro 's num

             =    1.9 X 10 23 / 6.02x10 23

              = 0.266 mole of Pb

now we calculate the mass

   mass of lead = # mol x m.wt

                       =    0.266 X 106.4

                       = 28.30 gram

your answer would be a. 12.5 kg

d.) circle motion requires a force to give it a centripetal acceleration.