Methanogens are most abundant in a

$Clostridium$ is an example of:

Which of the following are concerned with eubacteria?
$(1)$ Methanogens $(2)$ Anabaena $(3)$ $N_2$ fixation $(4)$ Thermoacidophiles $(5)$ Eukaryotes $(6)$ Diatoms $(7)$ Gelatinous sheath $(8)$ Heterocyst

In the bacterium $Bacillus$ $subtilis$,the cells often become attached from end to end forming long filamentous chains,which are embedded in a mass of mucilage forming a scum layer on the substratum. This is called:

Escherichia coli has the following combination of characters:

Which of the following is an example of a prokaryotic organism?