Element A has 15 protons. Determine the number of neutrons in its isotope with mass number 33

Can you guys me with question no. 5!

What is one real world example of a colligative property?

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