What type of microorganism is $Oscillatoria$?

Which of the following statements is correct for both blue-green algae and bacteria?

Select the correct statements from the given statements $(1-4)$ regarding the characteristics of some organisms.
$(1)$ Methanogens are Archaebacteria that produce methane in marshy areas.
$(2)$ $Nostoc$ is a flagellated blue-green alga that fixes atmospheric nitrogen.
$(3)$ Chemosynthetic autotrophic bacteria synthesize cellulose from glucose.
$(4)$ Mycoplasma lacks a cell wall and can survive without oxygen.

Gas vacuoles are found in:

Write a short note on Mycoplasma.

How many bacteria are produced in four hours if a bacterium divides once in half an hour?