Don't worry, I'm here to help!
Paramecium is indeed a member of the Protista kingdom, but it belongs to the phylum Ciliophora. It seems like the available options for classification that you have been given are from a different classification system. Chordate, Mollusk, Annelids, and Arthropod are actually phyla from the animal kingdom, while Paramecium belongs to the Protista kingdom, which includes various unicellular eukaryotic organisms.
To properly classify Paramecium, you should use the phylum Ciliophora. This phylum consists of organisms that possess cilia, which are hair-like structures used for locomotion and feeding. Paramecium is a single-celled organism that uses cilia to move and sweep food particles into its oral groove.
If the available classification options are limited to Chordate, Mollusk, Annelids, and Arthropod, none of these options are suitable for Paramecium since it does not belong to the animal kingdom. I would suggest bringing this issue to your teacher or instructor, as it seems there may be a mistake in the provided options.