Which of the following fourth period elements are paramagnetic: Ca, Mn, Co, Se, and Kr?

• A. Mn, Co, and Se
• B. Mn and Co only
• C. Ca and Kr only
• D. All except Kr

Answer: (A)

Verified step by step guidance

1. Recall that an element is paramagnetic if it has one or more unpaired electrons in its electron configuration.
2. Write the electron configurations for each element in the fourth period: Ca, Mn, Co, Se, and Kr. Use the Aufbau principle, Hund's rule, and the Pauli exclusion principle to determine the distribution of electrons.
3. Identify the number of unpaired electrons in each element's electron configuration. For example, look at the 3d and 4p subshells where unpaired electrons are most likely to appear in these elements.
4. Determine which elements have unpaired electrons (paramagnetic) and which have all electrons paired (diamagnetic).
5. Conclude that Mn, Co, and Se have unpaired electrons and are paramagnetic, while Ca and Kr have all paired electrons and are diamagnetic.