HOW DID STUDENTS CHOOSE A TOPIC?
What you need to be aware of is that this essay contributes to your final IB grade, but can potentially be used for university applications as well. Students generally decide on a subject to write their essay in quite quickly, and based off their interests (keep in mind that interdisciplinary essays are also a possibility). The subject should correspond to one you take as a class, to ensure that you have enough knowledge of the required content.
To then find a topic, students can consider the following:
The topic should be one that allows for thorough research in closely related areas, but the exact investigation must be unique
The topic must allow for enough complexity, but cannot be in a level that students are unable to reach with their available resources and knowledge
Extended Essays in a science should involve further experiments that demonstrate knowledge of the topic and allow students to develop their own idea
The essay is, primarily, a research project. Ensure that there is enough information available (e.g., in the form of journal articles, scientific research papers or published data) that you can support your essay sufficiently with this information
Choose a topic which you will enjoy working on and that interests you as an area of study