Number of formula units in unit cell of MgO (rock salt), ZnS (zinc blende) and Pt (fcc) respectively

Options

A. `4, 3, 2`
B. `4, 3, 4`
C. `4, 4, 4`
D. `4, 3, 1`

Answer

To find the number of formula units in the unit cell of MgO (rock salt), ZnS (zinc blende), and Pt (face-centered cubic), we will analyze each compound step by step.

### Step 1: Determine the structure of MgO (Rock Salt)
- **Structure**: MgO crystallizes in a face-centered cubic (FCC) lattice structure.
- **Number of formula units (Z)**: In an FCC structure, there are 4 atoms per unit cell. Since MgO consists of one Mg²⁺ ion and one O²⁻ ion, the number of formula units in the unit cell is 4.

### Step 2: Determine the structure of ZnS (Zinc Blende)
- **Structure**: ZnS crystallizes in a zinc blende structure, which is also based on a face-centered cubic (FCC) lattice.
- **Number of formula units (Z)**: In the zinc blende structure, there are 4 Zn²⁺ ions and 4 S²⁻ ions in the unit cell, thus the number of formula units is also 4.

### Step 3: Determine the structure of Pt (Platinum)
- **Structure**: Platinum crystallizes in a face-centered cubic (FCC) structure.
- **Number of formula units (Z)**: Similar to MgO and ZnS, the FCC structure of platinum also contains 4 atoms per unit cell. Since it is a pure element, the number of formula units is 4.

### Final Answer:
- **MgO**: 4 formula units
- **ZnS**: 4 formula units
- **Pt**: 4 formula units

Thus, the number of formula units in the unit cell of MgO, ZnS, and Pt respectively is 4, 4, and 4.

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