Which is incorrect physical property order for the given alkaline earth metals?

Options

A. Metallic radius : `Ba gt Sr gt Ca gt Mg gt Be`
B. Reducing nature : `Ba Sr gt Ca gt Mg gt Be`
C. Density : Ba > Sr > Be > Mg > Ca
D. Negative hydration enthalpy : `Be^(2+) gt Mg^(2+)gt Ca ^(2+)gt Ba^(2+) gt Sr^(2+)`

Answer

To determine the incorrect physical property order for the given alkaline earth metals, we need to analyze the properties of the alkaline earth metals systematically. The alkaline earth metals include Beryllium (Be), Magnesium (Mg), Calcium (Ca), Strontium (Sr), and Barium (Ba).

### Step 1: Analyze the Metallic Radius
- As we move down the group from Beryllium to Barium, the number of electron shells increases, leading to an increase in atomic size.
- Therefore, the order of metallic radius is:
- Ba > Sr > Ca > Mg > Be

**Hint:** Remember that the size of the atom increases with the addition of electron shells.

### Step 2: Analyze the Reducing Nature
- The reducing nature of alkaline earth metals increases down the group. This is because the tendency to lose electrons increases.
- Thus, the order of reducing nature is:
- Ba > Sr > Ca > Mg > Be

**Hint:** Consider how easily each metal can lose electrons to form positive ions.

### Step 3: Analyze the Density
- The density of alkaline earth metals initially decreases from Beryllium to Calcium and then increases from Calcium to Barium.
- The correct order for density is:
- Ba > Sr > Mg > Be > Ca

**Hint:** Think about how atomic mass and packing affect density.

### Step 4: Analyze the Negative Hydration Enthalpy
- Hydration enthalpy decreases as the size of the cation increases. Therefore, the order for negative hydration enthalpy is:
- Be > Mg > Ca > Sr > Ba

**Hint:** Remember that smaller ions have higher hydration enthalpy due to stronger interactions with water molecules.

### Conclusion
Now, let’s check the provided options for the incorrect order:

1. **Metallic Radius:** Ba > Sr > Ca > Mg > Be (Correct)
2. **Reducing Nature:** Ba > Sr > Ca > Mg > Be (Correct)
3. **Density:** Ba > Sr > Mg > Be > Ca (Incorrect, should be Ba > Sr > Ca > Mg > Be)
4. **Negative Hydration Enthalpy:** Be > Mg > Ca > Sr > Ba (Correct)

The incorrect order is found in the density option (Option 3).

### Final Answer
The incorrect physical property order for the given alkaline earth metals is **Option 3** (Density).

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