Which element has an atom with a nucleus containing 56 protons and 82 neutrons?

• A. Lanthanum (La)
• B. Strontium (Sr)
• C. Barium (Ba)
• D. Cesium (Cs)

Answer: (C)

Verified step by step guidance

1. Identify the number of protons in the nucleus, which corresponds to the atomic number (Z) of the element. Here, the nucleus contains 56 protons, so Z = 56.
2. Recall that the atomic number uniquely identifies an element on the periodic table. Find the element with atomic number 56.
3. Calculate the mass number (A) of the atom by adding the number of protons and neutrons: \(A = Z + N = 56 + 82\).
4. Use the atomic number to look up the element on the periodic table. The element with atomic number 56 is Barium (Ba).
5. Confirm that the isotope described is an isotope of Barium with mass number equal to the sum of protons and neutrons, which matches the given nuclear composition.