Which of the following species has the largest atomic or ionic radius?

• A. K^+
• B. Na
• C. K
• D. Na^+

Answer: (C)

Verified step by step guidance

1. Step 1: Understand that atomic and ionic radius refer to the size of an atom or ion, which depends on the number of electrons and the effective nuclear charge experienced by those electrons.
2. Step 2: Identify the species given: K⁺ (potassium ion), Na (neutral sodium atom), K (neutral potassium atom), and Na⁺ (sodium ion).
3. Step 3: Recall that cations (positive ions) have fewer electrons than their neutral atoms, leading to a smaller radius due to less electron-electron repulsion and a stronger pull from the nucleus.
4. Step 4: Compare the species by considering their electron configurations and nuclear charge: neutral atoms generally have larger radii than their corresponding cations, and among neutral atoms, those with more electron shells have larger radii.
5. Step 5: Conclude that the neutral potassium atom (K) has more electron shells than sodium and is not missing electrons like the cations, so it will have the largest atomic or ionic radius among the options.