Which of the following ions is not univalent?

Options

A. ammonium
B. nitrite
C. bicarbonate
D. sulphite

Explanation

To determine which of the following ions is not univalent, we need to understand the concept of valency and how it applies to ions.

### Step-by-Step Solution:

1. **Understand Valency**:
- Valency refers to the combining capacity of an element, which can also be understood in terms of the charge on the ion.
- Ions can have either a positive or negative charge.

2. **Identify Univalent Ions**:
- Univalent (or monovalent) ions have a charge of ±1. This means they can either lose or gain one electron.
- Examples of univalent ions include:
- Ammonium (NH₄⁺) has a charge of +1.
- Nitrite (NO₂⁻) has a charge of -1.
- Bicarbonate (HCO₃⁻) has a charge of -1.

3. **Identify Polyvalent Ions**:
- Polyvalent ions have a charge greater than ±1.
- For instance, the sulfide ion (SO₃²⁻) has a charge of -2, which makes it bivalent (divalent).

4. **Analyze the Given Ions**:
- Compare the charges of the ions provided:
- Ammonium (NH₄⁺): +1 (univalent)
- Nitrite (NO₂⁻): -1 (univalent)
- Bicarbonate (HCO₃⁻): -1 (univalent)
- Sulfide (SO₃²⁻): -2 (not univalent)

5. **Conclusion**:
- The ion that is not univalent is the sulfide ion (SO₃²⁻) because it has a charge of -2, which is greater than ±1.

### Final Answer:
The ion that is not univalent is **sulfide (SO₃²⁻)**.