An atom has an atomic mass of 28 and contains 14 neutrons. What element is it?

• A. Magnesium (Mg)
• B. Aluminum (Al)
• C. Phosphorus (P)
• D. Silicon (Si)

Answer: (D)

Verified step by step guidance

1. Recall that the atomic mass (also called mass number) of an atom is the sum of the number of protons and neutrons in its nucleus: \(\text{Atomic Mass} = \text{Number of Protons} + \text{Number of Neutrons}\).
2. Given the atomic mass is 28 and the number of neutrons is 14, use the formula to find the number of protons: \(\text{Number of Protons} = 28 - 14\).
3. Calculate the number of protons, which is equal to the atomic number of the element. The atomic number uniquely identifies the element on the periodic table.
4. Look up the element on the periodic table that has the atomic number equal to the number of protons you found.
5. Identify the element corresponding to that atomic number. This will give you the correct element for the atom with atomic mass 28 and 14 neutrons.