Answer:
9 protons
10 neutrons
9 electrons
Step-by-step explanation:
F is fluorine, element number 9. The element number is the number of protons in the atom: 9 protons.
19 is the atomic mass of 1 atom, made up of protons and neutrons, all having a mass of 1 AMU.
Since there are 9 protons, and electrons have a mass too small to make a difference at this level, an atomic mass of 19 means there must be (19 - 9) = 10 neutrons.
This is a neutral atom, so the number of electrons, at -1 charge each, must be equal to the number of protons, at +1 charge each. There are 9 protons, so there are also 9 electrons.