Final answer:
The correct word to fill in the blank is 'dropping,' signifying the student's intention to discontinue their chemistry class due to boredom.
Step-by-step explanation:
The correct answer to the question “I’m thinking about _____ chemistry next year because I’m finding it very boring.” is option b. dropping. The sentence is expressing the student's lack of interest in continuing with chemistry class in the future. Dropping is the term commonly used when one intends to discontinue a class or a subject. None of the other options provided (enrolling, failing, or sitting) would appropriately convey the meaning that the student no longer wishes to take the class due to lack of interest.