An element X has two isotopes. X–15 has 7 protons and 8 neutrons. Determine the atomic number and mass number of the second isotope, which has 10 neutrons in its nucleus.
a. atomic number = 8; mass number = 9
b. atomic number = 8; mass number = 17
c. atomic number = 7; mass number = 17
d. atomic number = 7; mass number = 15