Atomic structure of isotopes Steps:

• Atomic number of Ge is 32, so this neutral Ge atom has 32 protons, 32 electrons, and 70 - 32 = 38 neutrons.
• Se has atomic number 34; neutral Se has 34 electrons, so Se^{2-} ion gains 2 electrons for 36 total.
• Zn has atomic number 30, so ^{74}Zn atom has 74 - 30 = 44 neutrons.
• Gd has atomic number 64, so a neutral Gd atom has 64 protons. Why C is correct:
• The atomic number equals the number of protons; half of Gd's 64 protons is 32, matching Ge's protons. Why the others are wrong:
• A: Ge atom has 32 electrons, but Se^{2-} has 36 electrons (34 protons + 2 extra electrons).
• B: Ge-70 has 38 neutrons, but ^{74}Zn has 44 neutrons. Final answer: C