To find the mass number of an atom, you add the number of protons and neutrons together.
In this case:
- Protons = 19
- Neutrons = 20
Mass number = Protons + Neutrons = 19 + 20 = 39
Therefore, the mass number of the atom is 39.
Matter Interactions Online Practice
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Question
An atomic model shows 19 protons, 20 neutrons, and 19 electrons. What is the mass number of the atom?(1 point)
Responses
19
19
58
58
20
20
39
1 answer