Which of the following elements has only one valency?

Options

A. Phosphorous
B. Iron
C. Oxygen
D. Nitrogen

Answer

To determine which of the following elements has only one valency among phosphorus, iron, oxygen, and nitrogen, we will analyze each element's valency step by step.

### Step 1: Understand Valency
Valency is defined as the combining capacity of an element, which indicates how many electrons an atom can lose, gain, or share when forming chemical bonds.

### Step 2: Analyze Phosphorus
- **Element**: Phosphorus (P)
- **Atomic Number**: 15
- **Electronic Configuration**: 1s² 2s² 2p⁶ 3s² 3p³
- **Valency**: Phosphorus has 5 electrons in its outer shell (3s² 3p³). To complete its octet, it can gain 3 electrons or lose 5 electrons. Therefore, phosphorus can exhibit a valency of 3 (gaining 3 electrons) or 5 (losing 5 electrons).

### Step 3: Analyze Iron
- **Element**: Iron (Fe)
- **Atomic Number**: 26
- **Electronic Configuration**: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁶
- **Valency**: Iron can lose 2 electrons from the 4s subshell or lose 3 electrons (2 from 4s and 1 from 3d). Thus, iron can exhibit a valency of either 2 or 3.

### Step 4: Analyze Oxygen
- **Element**: Oxygen (O)
- **Atomic Number**: 8
- **Electronic Configuration**: 1s² 2s² 2p⁴
- **Valency**: Oxygen has 6 electrons in its outer shell. To complete its octet, it can gain 2 electrons. Therefore, the valency of oxygen is 2.

### Step 5: Analyze Nitrogen
- **Element**: Nitrogen (N)
- **Atomic Number**: 7
- **Electronic Configuration**: 1s² 2s² 2p³
- **Valency**: Nitrogen has 5 electrons in its outer shell. To complete its octet, it can gain 3 electrons. However, nitrogen can also share its lone pair, which can allow it to exhibit a valency of 4 in some compounds.

### Step 6: Conclusion
After analyzing all four elements:
- Phosphorus has a valency of 3 or 5.
- Iron has a valency of 2 or 3.
- Oxygen has a valency of 2.
- Nitrogen has a valency of 3 or 4.

None of these elements exhibit only one valency. Therefore, the answer is that none of these elements have only one valency.

### Summary of Steps:
1. Understand the concept of valency.
2. Analyze the valency of phosphorus.
3. Analyze the valency of iron.
4. Analyze the valency of oxygen.
5. Analyze the valency of nitrogen.
6. Conclude that none of the elements have only one valency.