7. List the number of protons, neutrons, and electrons for an anion with a negative 3 charge if the neutral atom has an atomic number of 15 and mass of 31.
Answer: B
B) 15 protons, 16 neutrons, 18 electrons
An anion with a negative 3 charge indicates that it has gained three additional electrons compared to its neutral state. For an atom with an atomic number of 15, which corresponds to the number of protons, the anion would have 15 protons, 16 neutrons (derived from the difference between mass number and atomic number), and 18 electrons.
A) 12 protons, 31 neutrons, 15 electrons
This option incorrectly states the number of protons as 12, which does not match the atomic number of 15. Additionally, it inaccurately lists the number of neutrons as 31, which cannot be reconciled with the atomic number provided.
B) 15 protons, 16 neutrons, 18 electrons
This option correctly identifies the number of protons as 15, corresponding to the atomic number. It also accurately lists the neutrons as 16, calculated by subtracting the atomic number from the mass number (31 - 15 = 16), and accounts for the three additional electrons due to the negative 3 charge, resulting in a total of 18 electrons.
C) 15 protons, 16 neutrons, 15 electrons
While this option correctly lists the protons and neutrons, it incorrectly states the number of electrons. Since the anion has a negative charge of 3, it must have 18 electrons, not 15.
D) 15 protons, 16 neutrons, 12 electrons
This option accurately states the protons and neutrons but incorrectly states the number of electrons. The negative charge indicates that the anion has gained electrons, resulting in a total of 18 electrons rather than 12.
Conclusion
Option B is the only choice that accurately reflects the properties of the anion based on the given atomic number and mass number. All other options fail due to incorrect counts of protons, neutrons, or electrons, making B the definitive correct answer.