Radiation is the emission of energy as electromagnetic waves or especially high-energy particles which cause ionization. It is not necessary that the source of heat must be a liquid. Most of the time radiation is produced from a solid substance which burns with a high amount of temperature. That temperature is transferred to the surroundings in the form of electromagnetic waves and they do not require any medium to propagate.
Well Primary Succession means you are the first organisms of that area after it is destroyed completely or if it's new. Secondary Succession is when an area is not destroyed completely but the organisms that remain colonize the area again. I believe it's C.
