The atomic mass of an element is a. the sum of the protons and neutrons in one atom of the element. b. twice the number of protons in one atom of the element. c. a ratio based on the mass of a carbon-12 atom. d. a weighted average of the masses of an element’s isotopes.

The atomic mass of an element is D. a weighted average of the masses of an element’s isotopes.

The sum of the protons and neutrons in one atom of the element is the mass number.

A ratio based on the mass of a carbon-12 atom gives the atomic mass in unified atomic mass units (u),

a electronegativity decreases beacuse the size of nucleus is bigger.