Which of the following prokaryotes are most abundant in nature and are helpful in making curd from milk and in the production of antibiotics?

Which of the following statements is true for Mycoplasma?

Cells of $Nostoc$ are

The length of $Mycobacterium$ $tuberculosis$ is: (in $\mu m$)

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.

$Thermococcus$,$Methanococcus$ and $Methanobacterium$ exemplify: