Which noble gas isotope has exactly 48 neutrons?

• A. Xe-132
• B. Ne-20
• C. Kr-84
• D. Ar-40

Answer: (C)

Verified step by step guidance

1. Recall that the number of neutrons in an isotope is given by the difference between the mass number (A) and the atomic number (Z): \(\text{Number of neutrons} = A - Z\).
2. Identify the atomic number (Z) of each noble gas element from the periodic table: Neon (Ne) = 10, Argon (Ar) = 18, Krypton (Kr) = 36, Xenon (Xe) = 54.
3. Calculate the number of neutrons for each isotope by subtracting the atomic number from the mass number: For example, for Xe-132, neutrons = \$132 - 54$.
4. Perform this calculation for each isotope: Xe-132, Ne-20, Kr-84, and Ar-40, to find which one has exactly 48 neutrons.
5. Compare the calculated neutron numbers to 48 and identify the isotope that matches this number.