Which of the following is an algal parasite?

Select the correct option by matching Column-$I$ with Column-$II$.

Column-$I$	Column-$II$
$(A)$ Blue-green algae	$(p)$ Chlamydomonas
$(B)$ Unicellular algae	$(q)$ Spirogyra
$(C)$ Filamentous algae	$(r)$ Volvox
$(D)$ Colonial algae	$(s)$ Nostoc

The botanical name of the sea palm is:

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

In which of the following,all listed genera belong to the same class of algae?

What is the basis of classification of algae?