Why is it impossible for an element to have an atomic number of 110.5?

Question

A. Exactly half of isotopes would need an atomic number of 110, and half would an atomic number of 111, which is very unlikely
B. Atoms with atomic numbers greater than 100 are unstable
C. Atoms of an element all have the same whole number of protons and neutrons
D. The atomic number is the number of protons, which is always a whole number

Answer 1

The correct answer is D. The atomic number is the number of protons, which is always a whole number.

The atomic number of an element is defined as the number of protons in the nucleus of an atom of that element, and since protons are discrete particles, the atomic number must be a whole number. Thus, an atomic number of 110.5 is not possible because it is not an integer.