Carbon dioxide forms a snowy white solid called ..................... at -78°C.

Answer

**Step-by-Step Solution:**

1. **Understanding Carbon Dioxide**: Carbon dioxide is a colorless gas at room temperature and pressure. It is commonly known by its chemical formula CO2.

2. **Temperature Reference**: The question specifies a temperature of -78°C. This is a key point because it indicates the conditions under which carbon dioxide changes state.

3. **Phase Change of Carbon Dioxide**: At -78°C, carbon dioxide does not exist as a liquid under normal atmospheric pressure. Instead, it sublimates directly from gas to solid.

4. **Formation of Solid Carbon Dioxide**: When carbon dioxide gas is cooled to -78°C, it forms a solid. This solid is known for its snowy white appearance.

5. **Naming the Solid**: The snowy white solid formed from carbon dioxide at -78°C is commonly referred to as "dry ice."

6. **Properties of Dry Ice**: Dry ice is used for various applications, including refrigeration and creating fog effects. It is important to note that dry ice can cause skin burns due to its extremely low temperature.

**Final Answer**: Carbon dioxide forms a snowy white solid called **dry ice** at -78°C.

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