Laminarin and mannitol are stored food of $:-$

In the alternation of generations in algae,which phase is considered the secondary and resting stage?

What is a coenobium?

Sexual reproduction in $Spirogyra$ is considered an advanced feature because it shows:

Assertion : Red algae contribute to the production of coral reefs.
Reason : Some red algae secrete and deposit calcium carbonate over their walls.

Which of the following is the method of vegetative reproduction in algae?