How many protons, electrons, and neutrons does 18f- contain?

             Number of Protons  =  9

             Number of Neutrons  =  9

             Number of Electrons  =  10

Number of Protons:

                               The number of protons present in any atom are equal to the atomic number of that particular atom. Hence, as the atomic number of Fluorine is 9 therefore, it contains 9 protons.

Number Neutrons:

                             The number of neutrons present in atom are calculated as,

                                # of Neutrons  =  Atomic Mass - # of protons

As given,

                                Atomic Mass  =  18

                                # of Protons  =  9

So,

                                # of Neutrons  =  18 - 9

                                # of Neutrons  =  9

Number of Electrons:

                                   As we know for a neutral atom the number of electrons are exactly equal to the number of protons present in its nucleus. So, for 9 protons in neutral Fluorine atom there must be 9 electrons. But, we are given with Fluoride Ion (i.e. F⁻) so it contains one extra electron hence, it contains the total of 10 electrons respectively.