An atom has 3 protons and 4 neutrons. Which isotope is it?

• A. Helium-7 (${\mathrm{He}}_7$)
• B. Lithium-6 (${\mathrm{Li}}_6$)
• C. Lithium-7 (${\mathrm{Li}}_7$)
• D. Beryllium-7 (${\mathrm{Be}}_7$)

Answer: (C)