Which of the following is a free-living,aerobic,non-photosynthetic,nitrogen-fixing bacterium?

The only group of organisms capable of using inorganic compounds as a source of energy is ........

Plant pathogenic bacteria are mostly .........

In prokaryotes,the photosynthetic lamellae remain in:

The nitrifying bacteria are

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