Final answer:
In an atom of magnesium-26, there are 12 protons and 14 neutrons. The number of neutrons is determined by subtracting the atomic number from the mass number, leading to the correct answer of 12 protons and 14 neutrons.
Step-by-step explanation:
The student's question is: How many protons (p) and neutrons (n) are in an atom of magnesium-26? The atom of an element is represented by its atomic number (the number of protons) and its mass number (the sum of protons and neutrons).
Magnesium's atomic number is 12, which means that every magnesium atom has 12 protons. The magnesium isotope specified in the question is magnesium-26. The '26' represents the mass number, which is the total number of protons and neutrons. To find the number of neutrons, we subtract the atomic number from the mass number: 26 (mass number) - 12 (protons) = 14 neutrons.
Therefore, the correct answer is d. 12 protons, 14 neutrons. This will be the nucleus of a magnesium-26 atom.