Which of the following is/are true statement(s)?

Options

A. On rising pressure coordination no. changes from 8:8 to 6:6
B. On rising temperature coordination no. changes from 8:8 to 6:6
C. Compounds with metal deficiency defect may behave as a p-type semiconductor
D. Compounds with metal excess defect may behave as a p-type semiconductor

Answer

To determine which of the given statements are true, let's analyze each statement step by step based on the principles of solid-state chemistry.

### Step 1: Analyze the first statement
**Statement 1:** "On rising pressure, coordination number changes from 8 to 6."

- **Explanation:** The coordination number is the number of nearest neighbors surrounding an atom in a crystal structure. According to the principles of solid-state chemistry, the coordination number generally increases with rising pressure because atoms are forced closer together. Therefore, this statement is **false**.

### Step 2: Analyze the second statement
**Statement 2:** "On rising temperature, coordination number changes from 8 to 6."

- **Explanation:** The coordination number typically decreases with increasing temperature due to increased atomic vibrations and thermal expansion, which can lead to a less dense packing of atoms. Thus, this statement is **true**.

### Step 3: Analyze the third statement
**Statement 3:** "Compounds with metal deficiency defect may behave as a p-type semiconductor."

- **Explanation:** A metal deficiency defect occurs when there are fewer metal ions than expected in a crystal lattice, which can create holes (positive charge carriers) in the material. This behavior is characteristic of p-type semiconductors, which are formed when a tetravalent semiconductor is doped with a trivalent element. Therefore, this statement is **true**.

### Step 4: Analyze the fourth statement
**Statement 4:** "Compounds with metal excess defect may behave as a p-type semiconductor."

- **Explanation:** A metal excess defect occurs when there are extra metal ions in the lattice, which typically leads to the creation of electrons (negative charge carriers), characteristic of n-type semiconductors. Therefore, this statement is **false**.

### Conclusion
Based on the analysis:
- Statement 1 is **false**.
- Statement 2 is **true**.
- Statement 3 is **true**.
- Statement 4 is **false**.

Thus, the true statements are **Statement 2 and Statement 3**.