Multinucleate decomposer organism is
Physarum is acellular slime moulds and are decomposers. It is multinucleate in its plasmodium stage. Pelomyxa is amoeboids and is multinucleated but not decomposer. Arcella is amoeba and are either uninucleate or binucleate. Dictyostelium are cellular slime moulds and bacterivores.
The correct answer is A.