Which of the following best describes a species with 7 protons, 7 neutrons, and 10 electrons?

• A. An isotope of oxygen with a 3- charge
• B. An anion of nitrogen with a 3- charge
• C. A neutral atom of nitrogen
• D. A cation of nitrogen with a 3+ charge

Answer: (B)

Verified step by step guidance

1. Identify the element by the number of protons. The number of protons defines the atomic number and thus the element. Here, the species has 7 protons, so it corresponds to nitrogen (atomic number 7).
2. Determine the number of neutrons to find the isotope. The isotope is identified by the sum of protons and neutrons, which gives the mass number. Here, 7 protons + 7 neutrons = mass number 14, so this is nitrogen-14.
3. Analyze the number of electrons to determine the charge. A neutral nitrogen atom has 7 electrons (equal to the number of protons). This species has 10 electrons, which is 3 more than protons, indicating a 3- charge.
4. Combine the information: element (nitrogen), isotope (mass number 14), and charge (3-). This describes an anion of nitrogen with a 3- charge, specifically the nitride ion (N³⁻).
5. Confirm that the other options do not match: oxygen has 8 protons, so it cannot have 7 protons; a neutral nitrogen atom would have 7 electrons; a cation with 3+ charge would have 4 electrons, not 10.