I would really appreciate help with the following, as I don't understand how to work it. Thank you in advance for explaining it to me.

The mass number (A) of a nuclide is equal to the number of --- blank --- in one of its nuclei. There are 4 answers to choose from: Protons, Neutrons, Protons+neutrons, or neutrons+electrons?

3 answers

The atomic number of an element tells you how many protons there are in the nucleus. The atomic number is the number on the periodic table that increases by 1 from one element to the next. Check it out. The mass number of an element is the number of nucleons for that element. Nucleons is not one of the answers listed in your problem but nucleons is a way of saying "protons + neutrons"' i.e., the total of what is in the nucleus.
Thank you, DrBob. I am not understanding what is meant by the "nuclide"?
Just substitute the word "element" or "nucleus" or "atom" for nuclide.