Spirogyra cells contain

Which of the following algae forms a motile colony?

Male gametes are flagellated in

$(i)$ Green algae occur in fresh water,brackish water,and salt water.
$(ii)$ Habitat of Brown algae: fresh water (rare),brackish water,and salt water.
$(iii)$ Some red algae are found in fresh water,mostly occur in salt water,and some are in brackish water.
$(iv)$ Most of the red algae are multicellular.
$(v)$ Red algae may occur in both well-lighted regions close to the water surface and also at great depths in oceans where light penetration is little.
$(vi)$ The cell wall of red algae consists of cellulose $+$ agar.
$(vii)$ $2-8$,equal and apical flagella in green algae.

The free-living,nitrogen-fixing cyanobacterium which also forms a symbiotic association with the water fern $Azolla$ is.......

Which of the following is correct for Chlorophyceae?