Among the given crystal, which is a covalent crystal?

Options

A. Rock salt
B. Dry ice
C. Quartz
D. Ice

Explanation

To determine which of the given crystals is a covalent crystal, we can follow these steps:

### Step 1: Understand the Types of Crystals
Crystals can be classified into several types based on the nature of the bonding between their constituent particles. The main types include:
- Ionic crystals
- Covalent (or network) crystals
- Metallic crystals
- Molecular crystals

### Step 2: Identify Covalent Crystals
Covalent crystals, also known as network solids, are characterized by a large network of atoms connected by covalent bonds. Examples include:
- Diamond (a form of carbon)
- Quartz (silicon dioxide, SiO2)

### Step 3: Analyze the Given Crystals
From the information provided:
1. **Quartz (SiO2)**: This is a covalent crystal. It has a giant covalent structure where each silicon atom is bonded to four oxygen atoms, and each oxygen atom is bonded to two silicon atoms, forming a 3D network.
2. **Rock Salt (NaCl)**: This is an ionic crystal. It consists of sodium and chloride ions held together by ionic bonds.
3. **Dry Ice (CO2)**: This is a molecular solid. In the solid state, CO2 molecules are held together by weak intermolecular forces (Van der Waals forces).
4. **Ice (H2O)**: This is also a molecular solid, where water molecules are held together by hydrogen bonds, which are stronger than Van der Waals forces but still not covalent bonds.

### Step 4: Conclusion
Among the given options, the only covalent crystal is **Quartz (SiO2)**.

### Final Answer
The covalent crystal among the given options is **Quartz (SiO2)**.

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