Hhheelllp me

How many neutrons does an element have if its atomic number is 50 and its mass number is 166

How many oxygen atoms are there in 3.15 moles of hcl manganese (iv) oxide, mno2

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