Which one is the largest unicellular organism?

Which of the following are the characters of dinoflagellates?
$(i)$ They are planktonic golden yellow algae with soap box like structure.
$(ii)$ They are marine biflagellated protista.
$(iii)$ They appear yellow,green,brown,blue and red in colour.
$(iv)$ The cell wall has stiff cellulose plates on the outer surface.
$(v)$ They are saprophytic (or) parasitic unicellular forms.

Which group includes diverse organisms that have an infectious spore-like stage in their life cycle?

The main cause of water blooms observed in rivers,lakes,and seas is .......

"Fire algae" belongs to which group?

Diatoms are