The red colour of 'Red Sea' is due to which of the following algae?

Which of the following components are present in the cell wall of algae?
$(1)$ Cellulose $(2)$ Protein $(3)$ Galactans $(4)$ Mannans $(5)$ Suberin
$(6)$ Pectin $(7)$ Hemicellulose $(8)$ Calcium carbonate

Batrachospermum is found in:

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

$A$ 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:

In $Spirogyra$,meiosis occurs in