Final answer:
An ion with 15 protons, 16 neutrons, and 18 electrons has three more electrons than protons, resulting in a charge of 3-. The charge is indicated by the difference in the number of protons and electrons.
Step-by-step explanation:
The charge on an ion is determined by the difference between the number of protons and electrons. An ion with 15 protons, 16 neutrons, and 18 electrons would have more electrons than protons. Since protons are positively charged and electrons are negatively charged, having more electrons than protons results in a negative charge.
To calculate the charge, we subtract the number of protons from the number of electrons. Since there are 15 protons and 18 electrons, the calculation would be 18 electrons - 15 protons = 3 extra electrons. These extra electrons give the ion a charge of -3. Therefore, the ion's charge is 3-.
The number of neutrons does not affect the charge of the ion. Neutrons are neutral particles, meaning they have no charge. They are important for the mass of the atom but not for its charge. The charge is always specified as a superscript on the right side of the element symbol.