It is c.
Hoped this helped.
~Bob Ross
I believe that the answer is A
The mass number of a nucleus (except Hydrogen) is: number of protons + number of neutrons.
A=Z+N
A=mass number=protons + neutrons.
Z=atomic number=number of protons.
N=number of neutrons.
In the case of Hydrogen it depends of isotope of Hydrogen .
the hydrogen has three isotopes,
protium : A=Z, because N=0
deuterium: A=Z+N; N=1
tritium: A=Z+N; N=2
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