When the atoms of a gas or vapor are excited, for instance by heating or by applying an electrical field, their electrons are able to move from their ground state to higher energy levels. This energy corresponds to particular wavelengths of light, and so produces particular colors of light.
A solid.
As you slowly go from the solid state to the gas, the molecules within spread farther and farther away.
It can reduce heat loss by heating water. Also plants are based on the dry process, and it’s much better for the environment rather than any other conventional process.