Most bacteria are . . . . . . .

Heterocysts are found in certain

Methanogens are present in the $\dots$ of the digestive tract of cattle.

The given characters are seen in which of the following group?
$(i)$ Unicellular,colonial,filamentous,symbiotic or free living.
$(ii)$ The colonies are surrounded by a gelatinous sheath.
$(iii)$ Some can fix atmospheric nitrogen in specialized cells called heterocysts.
$(iv)$ They often form blooms in water bodies.

The classification of $Monera$ is based on which of the following?

Maximum nutritional diversity is found in the group $........$.