Why are cnidarians a turning point for behavior

Anybody who knows ap biology, can you friend or message me

There is a liquid capsule inside a cup full of liquid. the cup full of liquid has salt in it and the liquid capsule has no salt in it. in which direction will the solvent flow? a. the salt does not have to move b. from the capsule to the larger cup c. equally between the capsule and the cup d. from the larger cup to the capsule

The image shows a group of fish. the type of social behavior shown in the image is called