The correct option is B Chlamydomonas
Chlamydomonas is simple, unicellular and motile fresh water algae. It is mainly found in fresh water rich in nitrogen salts and organic matter.
Ulothrix is a genus of non-branching filamentous green algae, generally found in fresh and marine water.
Spirogyra is a filamentous green algae.
Chara is a genus of multicellular algae.