Final answer:
A magnesium atom with a mass number of 25 contains 12 protons, 13 neutrons, and 12 electrons.
Step-by-step explanation:
A magnesium atom with a mass number of 25 contains:
- Protons: 12
- Neutrons: 13
- Electrons: 12
The atomic number of magnesium is 12, which represents the number of protons in the nucleus. The mass number of 25 represents the sum of protons and neutrons in the nucleus. To find the number of neutrons, subtract the atomic number from the mass number. In this case, 25 - 12 = 13 neutrons. Since magnesium is electrically neutral, it has the same number of electrons as protons.