What is dry ice? 

Solid carbon dioxide 

The correct answer is option 1. Solid carbon dioxide.

Dry ice is the common name for solid carbon dioxide (CO₂). It is called "dry ice" because it sublimates directly from a solid to a gas without passing through a liquid phase, leaving no liquid residue. Here's an explanation:

1. Formation:

Dry ice is formed by pressurizing and cooling gaseous carbon dioxide. Under normal atmospheric pressure, carbon dioxide does not exist as a liquid; it transitions directly from a gas to a solid at extremely low temperatures.

2. Sublimation:

Dry ice undergoes sublimation, a phase transition in which a substance transitions directly from a solid to a gas without passing through the liquid phase. This process occurs at temperatures above -78.5 degrees Celsius (-109.3 degrees Fahrenheit), which is the sublimation point of carbon dioxide at atmospheric pressure.

3. Properties:

Dry ice appears as a white, solid block or pellets. It is extremely cold, with a temperature of around -78.5 degrees Celsius (-109.3 degrees Fahrenheit), making it useful for various applications where very low temperatures are required.

4. Applications:

Dry ice is commonly used as a cooling agent in various industries, such as shipping and transporting perishable goods. It is also employed in scientific experiments, for creating special effects in the entertainment industry, and for cleaning processes (dry ice blasting). Due to its sublimation, it does not leave a liquid residue.

5. Safety Precautions:

Handling dry ice requires caution because of its extremely low temperature. Direct contact with skin can cause frostbite, so it is typically handled with gloves or tools. Additionally, dry ice should be used in well-ventilated areas to prevent the buildup of carbon dioxide gas.

In summary, dry ice is the solid form of carbon dioxide, and its unique properties, including sublimation at low temperatures, make it valuable for various practical applications.