The incorrect arrangement regarding the properties of the given species is :

Options

A. `Co^(3+) lt Fe^(3+) lt Cr^(3+) lt Sc^(3+) :` Stability in aqueous solution
B. `Sc lt Ti lt Cr lt Mn` : Number of oxidation states
C. `V^(2+) lt Cr^(2+) lt Mn^(2+) lt Fe^(2+)`: Paramagnetic behaviour
D. `Ni^(2+) lt Co^(2+) lt Fe^(2+) lt Mn^(2+)`, Ionic size

Answer

To solve the question regarding the incorrect arrangement of properties of the given species, we will analyze the properties of the species mentioned: Scandium (Sc), Chromium (Cr), Iron (Fe), and Cobalt (Co) in their +3 oxidation states.

### Step-by-Step Solution:

1. **Identify the Electron Configurations**:
- Scandium (Sc): [Ar] 3d¹ 4s² → Sc³⁺: 3d⁰
- Chromium (Cr): [Ar] 3d⁵ 4s¹ → Cr³⁺: 3d³
- Iron (Fe): [Ar] 3d⁶ 4s² → Fe³⁺: 3d⁵
- Cobalt (Co): [Ar] 3d⁷ 4s² → Co³⁺: 3d⁶

2. **Stability in Aqueous Solution**:
- The stability of these metal ions in aqueous solution can be assessed based on the number of unpaired electrons and the ability to coordinate with water molecules.
- Sc³⁺ has no unpaired electrons (3d⁰), making it highly stable.
- Cr³⁺ has 3 unpaired electrons (3d³), which is less stable than Sc³⁺ but more than Fe³⁺.
- Fe³⁺ has 5 unpaired electrons (3d⁵), making it less stable than Cr³⁺.
- Co³⁺ has 6 unpaired electrons (3d⁶), making it the least stable among these.

3. **Order of Stability**:
- Based on the analysis, the order of stability in aqueous solution is: Sc³⁺ > Cr³⁺ > Fe³⁺ > Co³⁺.

4. **Oxidation States**:
- Scandium can exhibit +2 and +3 oxidation states.
- Chromium can exhibit multiple oxidation states (+1, +2, +3, +4, +5, +6).
- Iron can exhibit +2 and +3 oxidation states.
- Cobalt can exhibit +2 and +3 oxidation states.
- Manganese (Mn) can exhibit +2, +3, +4, +5, +6, and +7 oxidation states.

5. **Order of Oxidation States**:
- The maximum oxidation states in order are: Mn > Cr > Fe > Sc.

6. **Paramagnetic Behavior**:
- Paramagnetism is determined by the number of unpaired electrons:
- V²⁺: 3 unpaired electrons (3d³)
- Cr²⁺: 4 unpaired electrons (3d⁴)
- Mn²⁺: 5 unpaired electrons (3d⁵)
- Fe²⁺: 4 unpaired electrons (3d⁶)
- The order of paramagnetism is: Mn²⁺ > Cr²⁺ = Fe²⁺ > V²⁺.

7. **Size Comparison**:
- The ionic size generally decreases across a period due to increased nuclear charge.
- The order of ionic sizes for the given ions is: Mn²⁺ > Fe²⁺ > Co²⁺ > Ni²⁺.

8. **Identify the Incorrect Arrangement**:
- From the analysis, the incorrect arrangement is related to the paramagnetic behavior where the order should be Mn²⁺ > Cr²⁺ > Fe²⁺ > V²⁺, but the question suggests a different order which is incorrect.

### Conclusion:
The incorrect arrangement regarding the properties of the given species is related to the paramagnetic behavior.