Atoms of which two elements have a combined total of 23 protons? A. Sodium, Na, and magnesium, Mg
B. Boron, B, and carbon, C
C. Copper, Cu, and zinc, Zn
D. None of these

A

Explanation:

Sodium has 11 electrons and Magnesium has 12 electrons. Since here you need to consider atoms, they must have equal amount of protons as electrons to be considered neutral, and so an atom.

So simply 11+12 =23