An unknown substance is a white solid at room temperature and has a melting point of 78 °C. Which of the following substances is most likely to be the identity of the unknown sample?

The comparison of the number of atoms in a copper coin the size of a penny with the number of people on earth is made to illustrate which of the following? a. that atoms are indivisible b. that atoms are very small c. that atoms are very large d. that in a copper penny, there is one atom for every person on earth