Citrus canker is caused by which of the following?

Nostoc is named after which of the following scientists?

Which domain includes well-known pathogenic organisms?

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

Blue-green algae show the closest resemblance to which of the following?

Which organisms obtain energy from the oxidation of reduced inorganic compounds?