It seems that your question is incomplete, and I can't see the list of options from which I should select the correct answer. However, based on the context you've provided, the word that could appropriately fill in the blank would likely be "infect" or "permeate."
So, the sentence could read: "Something was going terribly wrong in the science lab, and the smell was beginning to permeate the other classrooms on the..."
If you can provide the list of options, I'd be happy to help you choose the most appropriate one.