Read the possible answers. Remember these answers are given as a reference. It doesn't mean that your answers are incorrect

1. A chemical explosion is an odd word because it denotes a man-made disaster while all the rest denote natural disasters.
2. Pollution is an odd word because it denotes an environmental problem while all the rest denote social problems.
3. Rising sea levels is an odd phrase because it doesn't have to do with environmental problems related to plants like the rest of the words.
4. Authentic is an odd word because the rest of the words are synonyms denoting not harmful to the environment.
5. Harmful is an odd word because it denotes causing harm while all the rest denote weak, suffering from harm or already harmed.