Final answer:
The LFU page replacement algorithm is used because an actively used page should have a large reference count, which means it's less likely to be replaced when new pages are loaded into memory.
Step-by-step explanation:
The reason for using the LFU (Least Frequently Used) page replacement algorithm is (a) an actively used page should have a large reference count. LFU is a page replacement algorithm used in computer systems to manage memory. This algorithm works by keeping track of the number of times a page is accessed, which is called the reference count.
Pages with smaller reference counts are considered less frequently used and are more likely to be replaced when a new page needs to be loaded into memory. The idea is that pages that are accessed more often are likely to be needed again in the near future, whereas pages that are accessed less are more likely to be candidates for replacement.
Although LFU does have its advantages, it is not extremely efficient and optimal in all cases (c) and the assertion that a less used page has more chances to be used again (b) is generally not true for LFU since it prioritizes frequently accessed pages. Therefore, (d) All of the mentioned is not a correct answer because not all of the mentioned reasons are valid for using LFU.