One of these things is not like the others
Please go to the Question #13 post if you haven't had a chance work on this one yet, since the text below contains the solution.
For such common words, it may be surprising that the answer involves something rather arcane. Three of the items on the list are types (or "flavors") of quarks -- subatomic particles not believed to have any further sub-structure.
Up and down quarks are by far the most common. The four other types are up, down, strange, and charm. The word on the list which is NOT a quark type is "odd", so it does not belong. It is not like the others.