The correct words to fill in the blanks are:
- "respite" - The correct word in this context is likely "respire," which means to breathe.
- "percolate" - This is correctly used in the context of the smell spreading.
So the revised sentence would read:
"One by one, the students in the classroom next to the science lab began to look up and respire deeply at first and then quickly cover their noses. Something was going terribly wrong in the science lab, and the smell was beginning to percolate the other classrooms on the hall."
If you need further assistance or clarification, feel free to ask!