How can solid Carbon dioxide be directly converted into gaseous state ?

Which can be directly converted into solid state from gaseous state

Solid carbon dioxide is converted directly Into gaseous state when the pressure is decreased to :

A and B are the two solid substances. On heating they directly changes into gaseous state without undergoing liquid state. Name these two substances, and by what name this process is called?

How is carbon dioxide important?

Plants get carbon dioxide from

A solid organic compound X, on heating, directly converted into the vapour phase which on cooling solidifies. The best method for purifying X is

A solid directly changing Into vapour

Plants use Carbon dioxide for the process of

These organism obtain oxygen and expel carbon dioxide directly from the body by the process of diffusion