which of the following is not true about the ionic solids ?

Options

A. Bigger ions form the close packed structure
B. Smaller ions occupy either the tetrahedral or the octahedral voids depending upon their size
C. Occupation of all the voids is not necessary
D. The fraction of octahedral or tetrahedral voids occupied depends upon the radii of the ions occupying the voids .

Explanation

To determine which statement is not true about ionic solids, let’s analyze each option step by step:

### Step 1: Analyze the first statement
**Statement:** "Bigger ions form the close packed structure."
- In ionic solids, the larger ions (usually anions) do indeed form a close-packed structure. The smaller ions (cations) fit into the interstitial spaces (voids) created by the larger ions.
- **Conclusion:** This statement is true.

### Step 2: Analyze the second statement
**Statement:** "Smaller ions occupy either the tetrahedral or the octahedral voids depending upon their sizes."
- Smaller cations can occupy the tetrahedral or octahedral voids in the close-packed structure formed by the larger anions. The choice of void depends on the relative sizes of the ions.
- **Conclusion:** This statement is true.

### Step 3: Analyze the third statement
**Statement:** "Occupation of all the voids is not necessary."
- It is correct that not all voids in a crystal lattice need to be occupied. The occupation of voids depends on the stoichiometry and the size of the ions involved.
- **Conclusion:** This statement is true.

### Step 4: Analyze the fourth statement
**Statement:** "The fraction of octahedral or tetrahedral voids occupied depends upon the radii of the ions occupying the void."
- This statement is misleading because while the size of the ions does influence the number of voids that can be occupied, it is not solely dependent on the radii of the ions. The overall stoichiometry and arrangement also play significant roles.
- **Conclusion:** This statement is not true.

### Final Conclusion
Based on the analysis, the statement that is **not true** about ionic solids is:
**D: The fraction of octahedral or tetrahedral voids occupied depends upon the radii of the ions occupying the void.**

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