Which of the following elements can have negative oxidation states.

Options

A. `Al`
B. `Ca`
C. `Fe`
D. `B`

Answer

To determine which of the given elements can have negative oxidation states, we need to analyze the tendency of each element to gain or lose electrons. Let's go through the elements one by one.

### Step-by-Step Solution:

1. **Understanding Negative Oxidation States**:
- Negative oxidation states occur when an element gains electrons. Therefore, we need to identify which elements have a tendency to gain electrons.

2. **Analyzing Each Element**:
- **Aluminium (Al)**:
- Aluminium is a metal and has the electronic configuration of [Ne] 3s² 3p¹.
- Metals typically lose electrons to achieve a stable electron configuration.
- Therefore, Aluminium cannot have a negative oxidation state as it tends to lose three electrons to form Al³⁺.

- **Calcium (Ca)**:
- Calcium is an alkaline earth metal with the electronic configuration of [Ar] 4s².
- Like other metals, calcium tends to lose electrons (in this case, two) to achieve a noble gas configuration.
- Thus, Calcium cannot have a negative oxidation state.

- **Iron (Fe)**:
- Iron is a transition metal with the electronic configuration of [Ar] 3d⁶ 4s².
- Iron can lose electrons to form positive oxidation states (+2 or +3) but does not gain electrons to form negative oxidation states.
- Therefore, Iron cannot have a negative oxidation state.

- **Boron (B)**:
- Boron is a non-metal with the electronic configuration of [He] 2s² 2p¹.
- As a non-metal, Boron has a high electronegativity and can gain electrons to achieve a stable configuration.
- Due to its small size and high electronegativity, Boron can accept an electron and exhibit a negative oxidation state.

3. **Conclusion**:
- Among the elements listed, only Boron can have a negative oxidation state.

### Final Answer:
The element that can have a negative oxidation state is **Boron (B)**.