What is a coenobium?

$A$: Most of the species of $Chara$ are monoecious but show cross-fertilization.
$R$: The plant body shows protandrous condition.

Which of the following shows the absence of chlorophyll $b$?

The giant algae or seaweeds belong to which class?

Laminarin and mannitol of class-$Phaeophyceae$ (brown algae) are:

The zygote containing $4$ meiospores in $Spirogyra$ is called