We need to remove 80 books of the same science.
First remove 50 on botany. did not reach target.
remove 65 on zoology. did not reach target.
remove 50 on geology. did not reach target.
remove 79 on physics. still need to remove 1 more book to reach 80 but what if the next 79 books are of chemistry.
so after removing 79 books of chemistry, there are 31 books left of chemistry and 11 books of physics.
so removing any 1 book of either subject will ensure that 80 books of the same science topic are removed.

Total number of books required = \(50+65+50+79+79+1 = 324\)

OA,E