Bacteria that retain the Gram stain are known as:

Under which of the following conditions does a Gram-positive bacterium appear Gram-negative?

Methanogens belong to which group of bacteria?

The content of mucopeptide (peptidoglycan) in the cell wall is higher in which of the following?

Select the correct statements from the given statements $(1-4)$ regarding the characteristics of some organisms.
$(1)$ Methanogens are Archaebacteria that produce methane in marshy areas.
$(2)$ $Nostoc$ is a flagellated blue-green alga that fixes atmospheric nitrogen.
$(3)$ Chemosynthetic autotrophic bacteria synthesize cellulose from glucose.
$(4)$ Mycoplasma lacks a cell wall and can survive without oxygen.

Which of the following statement$(s)$ is/are correct for bacteria?