Question: In FIFO page replacement algorithm, when a page must be replaced

Answer:

In the FIFO (First-In-First-Out) page replacement algorithm, the oldest page is chosen for replacement. This means that the page that has been in memory the longest (i.e., the one that was loaded first) will be replaced when a page fault occurs and a new page needs to be brought into memory. Therefore, the correct option is 1. oldest page is chosen.