Taking into account the definition of mass number, the correct option is the option A: the atomic mass of the atom is 39.
First of all, all atoms are made up of subatomic particles: protons and neutrons, which are part of their nucleus, and electrons, which revolve around them. Protons are positively charged, neutrons are neutrally charged, and electrons are negatively charged (electrons).
On the other hand, the mass number tells us the total number of particles in the nucleus. That is, the mass number is the sum of the number of protons and the number of neutrons in the atomic nucleus:
Mass number = (number of protons) + (number of neutrons)
It is represented by the letter A.
In this case:
- number of protons= 19
- number of neutrons= 20
So:
Mass number = 19 + 20
Solving:
Mass number= 39
In summary, the correct option is the option A: the atomic mass of the atom is 39.
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