Which element has a mass number of 100 and contains 56 neutrons in its nucleus?

• A. Ruthenium (Ru)
• B. Tin (Sn)
• C. Molybdenum (Mo)
• D. Palladium (Pd)

Answer: (A)

Verified step by step guidance

1. Recall that the mass number (A) of an element is the sum of the number of protons (Z) and neutrons (N) in its nucleus, expressed as \(A = Z + N\).
2. Given the mass number \(A = 100\) and the number of neutrons \(N = 56\), use the formula to find the number of protons: \(Z = A - N = 100 - 56\).
3. Calculate the number of protons \(Z\), which corresponds to the atomic number of the element. This atomic number identifies the element on the periodic table.
4. Look up the element with atomic number \(Z\) on the periodic table to determine which element has 56 protons.
5. Confirm that the element with atomic number \(Z\) and mass number 100 is one of the options given, and select the correct element accordingly.