Question 3.1: An atom has an atomic number of 9 and a mass number of 19. a......

a. There are 9 protons because the atomic number is always equal to the number of protons present.
b. There are 10 neutrons because the number of neutrons is always obtained by subtracting the atomic number from the mass number (19 – 9 = 10).
\quad\quad\quad\quad \underbrace{(Protons+neutrons)}_{Mass  number}-\underbrace{protons}_{Atomic  number}=neutrons
c. There are 9 electrons because the number of protons and the number of electrons are always the same in an atom.