Final answer:
To determine the number of electrons in an atom with a mass number of 28, 14 neutrons, and a net charge of -3, we find it has 14 protons (mass number minus neutrons) and must have 17 electrons to account for the extra negative charge.
Step-by-step explanation:
An atom with a mass number of 28, 14 neutrons, and a net charge of -3 requires a bit of calculation to find the number of electrons. The mass number is the sum of protons and neutrons. Since the atom has 14 neutrons, we can subtract 14 from 28, which gives us 14 protons. Each proton has a charge of 1+, and since the atom has a net charge of -3, this means it must have 3 more electrons than protons to achieve this negative charge. Thus, the atom has 14 (protons) + 3 (extra electrons to balance the -3 charge) = 17 electrons.