Which of the following substances has giant covalent structure

Options

A. Iodine crystal
B. Solid `CO_2`
C. Silica
D. White phosphorus

Explanation

To determine which of the given substances has a giant covalent structure, we can analyze each option based on their bonding characteristics.

### Step-by-Step Solution:

1. **Identify the Substances**: We need to consider the substances mentioned: iodine crystal, solid carbon dioxide, silica, and white phosphorus.

2. **Analyze Iodine Crystal**: Iodine (I2) is a diatomic molecule held together by van der Waals forces. It does not form a giant covalent structure as it consists of discrete molecules rather than a continuous network.

**Hint**: Look for the type of bonding and structure in the substance.

3. **Analyze Solid Carbon Dioxide**: Solid carbon dioxide (CO2) consists of discrete CO2 molecules held together by intermolecular forces. It does not have a giant covalent structure.

**Hint**: Check if the substance forms a continuous network or discrete molecules.

4. **Analyze Silica**: Silica (SiO2) has a giant covalent structure. It consists of a three-dimensional network of silicon and oxygen atoms bonded covalently. Each silicon atom is bonded to four oxygen atoms, creating a strong and extensive network.

**Hint**: Identify if the substance has a network of covalent bonds extending throughout the material.

5. **Analyze White Phosphorus**: White phosphorus (P4) consists of discrete P4 tetrahedral molecules. It does not form a giant covalent structure.

**Hint**: Consider if the substance is made of individual molecules or a continuous network.

6. **Conclusion**: Among the substances analyzed, only silica (SiO2) exhibits a giant covalent structure.

### Final Answer:
The substance that has a giant covalent structure is **silica (SiO2)**.