Question

Which of the following species will have the largest and the smallest sizes respectively? Na, Mg, $Na^{+}$, $Mg^{2+}$

• A. Mg and $Na^{+}$
• B. Mg and $Mg^{2+}$
• C. Na and $Mg^{2+}$
• D. Na and Mg
• E. $Na^{+}$ and Mg

Hint:

Cation size decreases as positive charge increases.

Answer 1

The Correct Option is C

Step 1: Concept
Atomic size decreases across a period; cation size is smaller than parent atom.

Step 2: Meaning
Higher positive charge on isoelectronic species results in smaller size.

Step 3: Analysis
Na is larger than Mg. $Mg^{2+}$ has more protons than $Na^{+}$ to pull the same number of electrons.

Step 4: Conclusion
Na is largest, $Mg^{2+}$ is smallest. Final Answer: (C)