To solve the question regarding the correct statements about defects in solids, let's analyze each option step by step.
### Step-by-Step Solution:
1. **Option 1: Schottky defect is shown by CsCl.**
- **Explanation:** A Schottky defect occurs when an equal number of cations and anions are missing from the lattice, maintaining electrical neutrality. CsCl, which has a high coordination number of 8, is known to exhibit Schottky defects. Therefore, this statement is **correct**.
2. **Option 2: Frenkel defect is shown by ZnS.**
- **Explanation:** A Frenkel defect occurs when an ion (usually a cation) is displaced from its lattice site to an interstitial site, creating a vacancy and an interstitial defect. ZnS, which has a low coordination number of 4, is known to exhibit Frenkel defects. Hence, this statement is also **correct**.
3. **Option 3: HCP and CCP structures have the same coordination number.**
- **Explanation:** Both Hexagonal Close Packing (HCP) and Cubic Close Packing (CCP) structures have a coordination number of 12. They also have the same packing efficiency of 74%. Thus, this statement is **correct**.
4. **Option 4: At high pressure, coordination number increases.**
- **Explanation:** Under high pressure, the structure of some ionic compounds can change, leading to an increase in coordination number. For example, NaCl has a coordination number of 6, but under high pressure, it can transform into a structure like CsCl, which has a coordination number of 8. Therefore, this statement is **correct**.
### Conclusion:
All four options are correct.
### Final Answer:
- **All options (1, 2, 3, and 4) are correct.**
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