Which element cannot form a cation ?

Options

A. Al
B. B
C. Cs
D. Bi

Answer

To determine which element cannot form a cation, we need to analyze the electronic configurations and properties of the given elements. Let's go through each option step by step.

### Step 1: Analyze Aluminium
- **Atomic Number**: 13
- **Electronic Configuration**: 1s² 2s² 2p⁶ 3s² 3p¹
- **Cation Formation**: Aluminium can lose three electrons (two from the 3s subshell and one from the 3p subshell) to form a cation with a +3 charge (Al³⁺).

### Step 2: Analyze Boron
- **Atomic Number**: 5
- **Electronic Configuration**: 1s² 2s² 2p¹
- **Cation Formation**: Boron has a high ionization energy due to its small size and high effective nuclear charge. It is difficult for boron to lose its three valence electrons to form a cation. Therefore, boron does not typically form a cation.

### Step 3: Analyze Cesium
- **Atomic Number**: 55
- **Electronic Configuration**: [Xe] 6s¹
- **Cation Formation**: Cesium is an alkali metal and can easily lose one electron from its 6s subshell to form a cation with a +1 charge (Cs⁺).

### Step 4: Analyze Bismuth
- **Atomic Number**: 83
- **Electronic Configuration**: [Xe] 4f¹⁴ 5d¹⁰ 6s² 6p³
- **Cation Formation**: Bismuth can lose electrons from both the 6s and 6p subshells to form cations, including a +5 charge (Bi⁵⁺).

### Conclusion
After analyzing all four elements, we find that boron is the only element that cannot form a cation due to its high ionization energy and small atomic size.

**Final Answer**: Boron (Option 2) cannot form a cation.

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