How many major ocean depths or trenches have been discovered in the Indian Ocean so far?

In which geographical area is the world's largest accumulation of marine plastic debris, known as the Great Pacific Garbage Patch, located?

Consider the following pairs: Oceanic Trench — Ocean I. Mariana Trench — Pacific Ocean II. Tonga Trench — Indian Ocean III. Peru-Chile Trench — Pacific Ocean IV. Puerto Rico Trench — Atlantic Ocean How many of the above pairs are incorrectly matched?