Which of the following is known as pond silk?

Which one of the following is an example of a chlorophyllous thallophyte?

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 forms are algae found?

Agranal chloroplasts are found in

$A$ research student collected a certain alga and found that its cells contained both chlorophyll $a$ and chlorophyll $d$,as well as phycoerythrin. The alga belongs to: