Question

what term refers to the unique number of protons in an elements nucleus? isotope number atomic number valence number atomic mass

Explanation:

The atomic number of an element is defined as the unique number of protons in the nucleus of an atom of that element. Isotope number is related to different forms of an element with varying neutrons. Valence number pertains to an atom's combining capacity. Atomic mass is the mass of an atom, which includes protons, neutrons and a small contribution from electrons.

Answer:

B. Atomic number