Which of the following groups secrete and deposit calcium carbonate and appear like corals?

The thallus of $Volvox$ is called

In $Gracilaria$,sexual reproduction is

The largest unicellular plant,$Acetabularia$,belongs to which of the following groups?

If you are asked to classify various algae into different groups,which of the following characteristics would you choose?

$A$ research student collects and observes some algae. The cells contain both chlorophyll $a, b, c$ and chlorophyll $d$,in addition to phycoerythrin. This alga belongs to: