Colourless, unicellular, cell wall bound spherical or rod-shaped microorganisms, lacking organized nucleus are

The correct option is A Bacteria
Bacteria belongs to prokaryotes, one of the 2 major groups. They are unicellular organisms that lack internal membrane-bound organelles. They do not have a true nucleus. Instead, they have the incipient nucleus called as nucleoid. Nucleoid is an irregularly shaped region that contains genetic material DNA. They are colourless. They have cell wall. They are either spherical, rod shaped or spiral in shape.

Thus, the correct answer is 'Bacteria.'