Question

but when she decided to address plastic pollution herself, anna didnt aim simply to remove the plastic bags, bottles, and toys that float on the oceans surface. her goal was more challenging. it was to help with something much less visible: microplastic.
what does the word it refer to?
was to help with something much less visible: microplastic.

Explanation:

To determine what "it" refers to, we analyze the context. The sentence before the one with "it" says "Her goal was more challenging." Then "It was to help with... microplastic." So "it" is a pronoun replacing the noun "goal" (specifically "Her goal") to avoid repetition. We check the structure: the first part introduces "Her goal" as the subject of being "more challenging", and then "it" continues to describe what that goal was (to help with microplastic).

Answer:

"it" refers to "Her goal" (Anna's goal to address plastic pollution, specifically the more challenging part of dealing with microplastic).