For hcp lattice which statements will be correct ?

Options

A. Coordination number of hcp =12
B. Volume of unit cell unoccupied =74%
C. It contains both tetrahedral and octahedral voids
D. This is more effective packing than ccp

Answer

To determine which statements about the hexagonal close packing (hcp) lattice are correct, we will analyze each statement step by step.

### Step 1: Understanding the Coordination Number
- The coordination number of a lattice is defined as the number of nearest neighbors surrounding a particular atom.
- In hcp, each atom is surrounded by 12 other atoms: 6 in the same layer, 3 in the layer above, and 3 in the layer below.

**Conclusion for Step 1:** The coordination number for hcp is 12.

### Step 2: Analyzing the Volume of the Unit Cell
- The packing efficiency of hcp is 74%. This means that 74% of the volume of the unit cell is occupied by the atoms.
- Therefore, the unoccupied volume in the unit cell is 100% - 74% = 26%.

**Conclusion for Step 2:** The statement claiming the unoccupied volume is 74% is incorrect; it is actually 26%.

### Step 3: Identifying the Types of Voids
- In hcp, there are both tetrahedral and octahedral voids present.
- Tetrahedral voids are formed when an atom is surrounded by four other atoms, while octahedral voids are formed when an atom is surrounded by six others.

**Conclusion for Step 3:** The statement that hcp contains both tetrahedral and octahedral voids is correct.

### Step 4: Comparing Packing Efficiency with CCP
- The packing efficiency of hcp (hexagonal close packing) is the same as that of CCP (cubic close packing), both being 74%.
- Therefore, the statement claiming that hcp has more effective packing than CCP is incorrect.

**Conclusion for Step 4:** The statement about hcp being more effective packing than CCP is incorrect.

### Final Summary of Correct Statements
- **Correct Statements:**
1. The coordination number of hcp is 12.
2. Hcp contains both tetrahedral and octahedral voids.

- **Incorrect Statements:**
1. The unoccupied volume of the unit cell is 74% (it is actually 26%).
2. Hcp has more effective packing than CCP (they have the same packing efficiency).