What is the phylum of octopus?

Octopus is an organism from the phylum Mollusca.

• Mollusca is a really big phylum consisting of many soft body organisms protecting their body with hard shell made of mantle but there are some organisms in this phylum who do not consists hard shell. 
• Octopus show all the characteristic features of Phylum Mollusca like they are invertebrate, triploblastic, bilaterally symmetrical, and found in various regions of the ocean.
• Some strategies that output follow to save himself from danger are ink explosion and blending with his surroundings.
• In animal kingdom arthropods is the largest phylum.

Hence, option B is the correct answer.