The radius of `Na^(+)` cation is less than that of Na atom. Give reason.

Explanation

To understand why the radius of the Na⁺ cation is less than that of the Na atom, we can break down the explanation into several steps:

### Step-by-Step Solution:

1. **Identify the Atomic Structure of Sodium (Na):**
- Sodium (Na) has an atomic number of 11, which means it has 11 electrons.
- The electronic configuration of sodium is:
\[ \text{Na: } 1s^2 \, 2s^2 \, 2p^6 \, 3s^1 \]

2. **Formation of Sodium Cation (Na⁺):**
- When sodium loses one electron to form a cation (Na⁺), it loses the single electron in the 3s orbital.
- The electronic configuration of Na⁺ becomes:
\[ \text{Na}^+: 1s^2 \, 2s^2 \, 2p^6 \]
- Now, Na⁺ has only 10 electrons.

3. **Understanding Atomic Radius:**
- The atomic radius is influenced by the number of electrons and the effective nuclear charge experienced by the outermost electrons.
- In Na, there are 11 electrons, and the outermost electron is in the 3s orbital, which experiences some shielding from the inner electrons.

4. **Effect of Losing an Electron:**
- When Na loses an electron to become Na⁺, the number of electrons decreases from 11 to 10.
- This results in a decrease in electron-electron repulsion among the remaining electrons.

5. **Increased Nuclear Attraction:**
- With one less electron, the remaining electrons experience a greater effective nuclear charge because there are still 11 protons in the nucleus attracting them.
- The reduced repulsion among the electrons allows the remaining electrons to be pulled closer to the nucleus.

6. **Conclusion:**
- As a result of the decreased electron-electron repulsion and increased attraction between the nucleus and the remaining electrons, the atomic radius of Na⁺ is smaller than that of the neutral Na atom.

### Final Answer:
The radius of Na⁺ is less than that of Na because the loss of one electron reduces electron-electron repulsion and increases the effective nuclear charge experienced by the remaining electrons, leading to a smaller atomic size.

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