Which one of the following oxides is ionic?

Options

A. `P_2O_5`
B. `CrO_3`
C. `MnO`
D. `Mn_2O_7`.

Answer

To determine which of the given oxides is ionic, we need to analyze each option based on the nature of the bonding involved, specifically looking for the presence of a metal and a non-metal, and the oxidation states of the elements involved.

### Step-by-Step Solution:

1. **Identify the Oxides**: The options provided are P2O5, CrO3, MnO, and Mn2O7.

2. **Analyze P2O5**:
- P2O5 consists of phosphorus (P) and oxygen (O), both of which are non-metals.
- Since both elements are non-metals, there is no ionic bond formed here.
- **Conclusion**: P2O5 is not ionic.

3. **Analyze CrO3**:
- CrO3 consists of chromium (Cr), a metal, and oxygen (O), a non-metal.
- To find the oxidation state of chromium:
- Oxygen has an oxidation state of -2.
- There are 3 oxygen atoms, contributing a total of -6.
- Therefore, for the compound to be neutral, chromium must have an oxidation state of +6.
- A +6 oxidation state indicates a high charge, leading to a significant covalent character according to Fajans' rule.
- **Conclusion**: CrO3 is not ionic.

4. **Analyze MnO**:
- MnO consists of manganese (Mn), a metal, and oxygen (O), a non-metal.
- The oxidation state of manganese in MnO is +2 (since oxygen is -2).
- A +2 oxidation state is not too high, allowing for a more ionic character in the bond.
- **Conclusion**: MnO is likely ionic.

5. **Analyze Mn2O7**:
- Mn2O7 consists of manganese (Mn) and oxygen (O).
- Let the oxidation state of manganese be X. The equation for the oxidation states is:
- 2X + 7(-2) = 0
- 2X - 14 = 0
- 2X = 14 → X = +7.
- A +7 oxidation state indicates a high charge, leading to a significant covalent character according to Fajans' rule.
- **Conclusion**: Mn2O7 is not ionic.

6. **Final Conclusion**:
- The only oxide that exhibits ionic character is **MnO**.

### Answer:
The oxide that is ionic is **MnO**.