It's in the very beginning of their question: it's the fast growing organism's choice. And a 24/7 coverage requirement is incredibly unlikely, considering the PI's expressed desire for the OP being at their desk 8/5.

Do you think their "own experiments" are things they are doing entirely for themself, and not part of the accepted work of the lab, but ones they are responsible for? I guess that's possible, but I think everyone else is assuming the latter is the case.

If you do interrupt, add "Unfortunately, I only have a limited time here today, and I think your question deserves more time than I have. But we'll have more time to go into it in detail after I've been hired here." [Give big smile to audience]. Of course, if you do get hired, you're sort of pre-committed to spending time with a possibly boring colleague.

Have you tried to read Newton's calculus? It's in a completely different language that most modern calculate classes, and requires a genius (like Newton) to understand it. Simply put, you're going to be behind a year or two most other incoming graduate students if you do that. A smart, motivated person can certainly make those up, but we shouldn't ignore the fact.

People are responsible for things they can't fully control all of the time. It's part of being an adult.

My name is "Jonathan", obviously. When giving my name when ordering food, "Jonathan" has extra syllables that can be inconvenient for the person entering the order. But there are too many Jon/Johns out there. So I picked "Jon Z" as my easy, uniquified name that I give at restaurants ... and, with variations, on web sites. Which is to say that I think this is a great idea.

Etymology does not trump usage.

As a metaphor: "It's like getting driving directions, and the review is to see if one would be able to get to their destination using the given directions. But we usually don't actually go out and drive to full route." And the "Personal Experience" story corresponds to "Wait, there's no off-ramp from I-95 to route 20! Gotta look closer at that part.".

This method would have to be used judiciously, but if he states something using language that is confusing (and you think is due to his non-native English based grammar), ask a question where you state it back with correct grammar. E.g. "In that last statement did you mean X Y Z?". You might get a grumpy "Yes. That is what I said." and the best you'll be able to respond is "Ah, sorry, it wasn't clear to me, and it sounded like maybe you meant Z Y X. Thank you for the clarification." Won't help on exams, and probably won't lead to him realizing the confusion he's causing, but might help a bit.

@EarlGrey - I disagree. That does more of the students work for them, and doesn't test their ability to identify a double displacement reaction. A blanket policy, stated in class before the test and also repeated on the test, of ""multiple answers may be true, but you need to pick the best, most specific, one", would be a better fix.

+1 for needing to clearly communicate expectations to students.

All we had to go on was the OP's statement that it "was also a correct answer". If, as it seems like, there are more facts in play, like one is less specific than the other, OP should have told us. In fact, if two instances make a pattern, this is now a pattern of OP not giving enough information for people to answer their questions well - once for their students in class and on the exam, and once for us here. Which is excellent, because having identified it, the OP now knows "I need to work on communicating more explicitly, with more details."

@FedericoPoloni - I probably wouldn't, but as to the distinction between "double displacement" and "neutralization", I'm very unqualified to make a judgement, which is why I left so much up to the OP....