Answer: The correct answer is -
Radial symmetry is a body plan of organisms where the body is divided into two equal parts by any plane that passes through the central axis (such as in Echinoderms and Coelentrates) of the body.
It is very useful for the sessile organisms (that are fixed or attached at one particular place through base) because there is an even distribution of sensory receptors in their body, which helps in detecting their threats (like predators) from all directions equally. Also, they can grab food from all direction equally by being attached to one place.