Blue-green algae belong to which of the following groups?

Which of the following lacks a well-defined nucleus?

Which of the following statements are incorrect for $Nostoc$ and $Anabaena$?
$(a)$. Possess tissue level organization
$(b)$. Have heterocysts
$(c)$. Can fix atmospheric hydrogen
$(d)$. They are eubacteria

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

Which of the following are likely to be present in deep-sea hydrothermal vents?

Most extensive metabolic diversity is found in $:-$