Which of the following represents the incoorect order of the properties indicated?

Options

A. `Ni^(2+)gtCr^(2+)gtFe^(2+)gtMn^(2+)` (size)
B. `ScgttIgtCrgtMn` (size)
C. `Ni^(2+)ltCo^(2+)ltFe^(2+)ltMn^(2+)` (unpaired electron)
D. `H_3AsO_4gtH_3PO_4` (acidic strength order)

Explanation

To solve the question, we need to analyze the given options to identify which one represents an incorrect order of the specified properties. Let's break down the analysis step by step.

### Step 1: Analyze Option 1
**Property**: Ionic Size Order of Chromium, Manganese, Iron, and Nickel in +2 oxidation state.

- **Expected Order**: The ionic sizes generally decrease across the d-block elements due to increasing nuclear charge.
- **Order**: Cr²⁺ > Mn²⁺ > Fe²⁺ > Ni²⁺ (This is the expected order based on ionic radii).

**Conclusion**: This order is correct, so Option 1 does not represent an incorrect order.

### Step 2: Analyze Option 2
**Property**: Electronegativity Order of Hc, Tr, Cr, Mn.

- **Expected Order**: Generally, electronegativity increases across a period and decreases down a group.
- **Order**: Hc > Cr > Mn > Tr (This order is based on the increasing electronegativity values).

**Conclusion**: This order is also correct, so Option 2 does not represent an incorrect order.

### Step 3: Analyze Option 3
**Property**: Unpaired Electrons in Mn²⁺, Fe²⁺, Co²⁺, and Ni²⁺.

- **Expected Order**: The number of unpaired electrons generally decreases as we move from left to right in the d-block.
- **Order**: Mn²⁺ (5 unpaired) > Fe²⁺ (4 unpaired) > Co²⁺ (3 unpaired) > Ni²⁺ (2 unpaired).

**Conclusion**: This order is correct, so Option 3 does not represent an incorrect order.

### Step 4: Analyze Option 4
**Property**: Acidic Strength of H₃AsO₄ and H₃PO₄.

- **Expected Order**: The acidic strength depends on the central atom and its electronegativity.
- **Order**: H₃PO₄ > H₃AsO₄ (Phosphorus is more electronegative than Arsenic, leading to stronger acidity).

**Conclusion**: The order given (H₃AsO₄ > H₃PO₄) is incorrect, making Option 4 the one that represents an incorrect order.

### Final Answer
The incorrect order of the properties indicated is represented by **Option 4**.

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