The correct answer is: Still air.
Air is a poor conductor of heat because it is made up of molecules that are very far apart. These molecules do not have a lot of energy, so they do not transfer heat very well.
Water is a better conductor of heat than air because its molecules are closer together. These molecules have more energy, so they transfer heat more easily.
Ice is a better conductor of heat than water because its molecules are arranged in a more orderly way. This allows them to transfer heat more easily.
Snow is a poor conductor of heat because it is made up of tiny ice crystals that are surrounded by air. These air pockets act as insulators, preventing heat from being transferred.
Soil is a poor conductor of heat because it is made up of a mixture of minerals, organic matter, and water. These materials do not transfer heat very well.
In conclusion, still air is the poorest conductor of heat because its molecules are very far apart and do not have a lot of energy.