The atomic number of nitrogen is 7. Nitrogen-15 has a greater mass number than nitrogen-14 because the atomic nucleus of nitrogen-15 contains ________.
a) 7 neutrons.
b) 8 neutrons.
c) 8 protons.
d) 15 protons.

• A. 7 neutrons.
• B. 8 neutrons.
• C. 8 protons.
• D. 15 protons.

Answer: (B)

Verified step by step guidance

1. Understand the concept of atomic number: The atomic number of an element is the number of protons in the nucleus of an atom of that element. For nitrogen, the atomic number is 7, meaning it has 7 protons.
2. Understand the concept of mass number: The mass number of an atom is the sum of the number of protons and neutrons in its nucleus. It is not the same as the atomic number.
3. Identify the isotopes: Nitrogen-14 and Nitrogen-15 are isotopes of nitrogen. Isotopes have the same number of protons but different numbers of neutrons.
4. Calculate the number of neutrons: For Nitrogen-14, the mass number is 14, and it has 7 protons. Therefore, it has 14 - 7 = 7 neutrons. For Nitrogen-15, the mass number is 15, and it has 7 protons. Therefore, it has 15 - 7 = 8 neutrons.
5. Determine the correct answer: Since Nitrogen-15 has a greater mass number due to having more neutrons than Nitrogen-14, the correct answer is that Nitrogen-15 contains 8 neutrons.