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, we need to analyze the characteristics of ionic solids and the options provided. Here’s a step-by-step solution:

### Step 1: Understand the Structure of Ionic Solids
Ionic solids are composed of positively charged ions (cations) and negatively charged ions (anions) that are arranged in a regular, repeating pattern. A common example is sodium chloride (NaCl), where Na⁺ and Cl⁻ ions alternate in a three-dimensional lattice.

**Hint:** Remember that ionic solids consist of cations and anions arranged in a specific geometric pattern.

### Step 2: Identify the Characteristics of Ionic Solids
1. **Size of Ions**: Anions (negatively charged ions) are generally larger than cations (positively charged ions).
2. **Electrical Conductivity**: Ionic solids are insulators in solid form but can conduct electricity when melted or dissolved in water because the ions are free to move.
3. **Void Occupation**: Cations occupy specific voids (tetrahedral or octahedral) in the lattice structure, depending on their size relative to the anions.
4. **Geometric Arrangement**: The occupation of voids depends on the geometry of the compound, not solely on the radii of the ions.

**Hint:** Focus on the properties of ionic solids, particularly how the size of ions affects their arrangement and conductivity.

### Step 3: Analyze the Given Options
Now, let’s evaluate the options provided in the question:

1. **Bigger ions form the close-packed structure.** (True)
2. **Smaller ions occupy either tetrahedral or octahedral voids.** (True)
3. **Occupation of all voids is not necessary.** (True)
4. **The fraction of octahedral or tetrahedral voids occupied depends on the radius of the ion occupying the hole.** (Not True)

**Hint:** Compare each statement with the characteristics of ionic solids. Look for the one that contradicts the established properties.

### Step 4: Conclusion
From the analysis, we find that the fourth statement is incorrect. The occupation of voids in ionic solids does not depend solely on the radius of the ions but rather on the geometry of the compound and the relative sizes of the ions.

**Final Answer:** The statement that is not true about ionic solids is the fourth one.

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