Question

sum of the number of protons and electrons in an atom is known as its mass number​

Answer 1

Answer:

The mass number (A) of an atom is the total number of protons and neutrons in its nucleus. The mass of the atom is a unit called the atomic mass unit (amu).

Explanation:

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Answer 2

Answer:

the mass number (symbol A, from the German word atomgewicht [atom weight ]).also called atomic mass number of nucleon number, is the total number of protons and neutrons (together known as nucleons) in an atomic nucleus... the mass number is different for each different isotope of chemical element.