The smallest cation and the smallest anion are respectively

Options

A. `H^(+)` and `H^(-)`
B. `H^(+)` and `F^(-)`
C. `Li^(+)` and `H^(-)`
D. `Li^(+)` and `F^(-)`

Answer

To determine the smallest cation and the smallest anion, we need to analyze the given options and understand the concepts of ionic size.

### Step 1: Identify the Cations
The options for cations are H⁺ and Li⁺.

- **H⁺ (Hydrogen cation)**: When hydrogen loses its one electron (from its 1s¹ configuration), it becomes H⁺, which has a configuration of 1s⁰. This means it has no electrons.
- **Li⁺ (Lithium cation)**: Lithium has an electron configuration of 1s² 2s¹. When it loses one electron to become Li⁺, its configuration becomes 1s², meaning it still has two electrons.

**Conclusion for Cations**: Since H⁺ has no electrons and Li⁺ has two, H⁺ is smaller than Li⁺. Therefore, the smallest cation is **H⁺**.

### Step 2: Identify the Anions
The options for anions are H⁻ and F⁻.

- **H⁻ (Hydride ion)**: When hydrogen gains an electron, it becomes H⁻. Its electron configuration is 1s², meaning it has two electrons.
- **F⁻ (Fluoride ion)**: Fluorine has an electron configuration of 1s² 2s² 2p⁵. When it gains one electron, it becomes F⁻ with a configuration of 1s² 2s² 2p⁶, which means it has ten electrons.

**Conclusion for Anions**: The size of an anion is generally larger than its parent atom due to increased electron-electron repulsion. In this case, H⁻ has two electrons and F⁻ has ten electrons. However, since H⁻ only has one proton to attract two electrons, it will not be as tightly held as F⁻, which has nine protons attracting ten electrons.

As we move across the periodic table from left to right, the size of the anions decreases. Therefore, H⁻ is larger than F⁻. Thus, the smallest anion is **F⁻**.

### Final Answer
The smallest cation is **H⁺** and the smallest anion is **F⁻**.

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