Question

what is the possessive form of the rooms of the students ​

Answer 1

Answer:

So, the possessive form of students (a plural noun that already ends with an -s) is students'. Think about the apostrophe as being a clue to the reader about number; in written work, the only way a reader knows whether or not you mean the possessive of one student or more than one student is by your use of the apostrophe.

The resource which I linked below is a very good tool for this and other grammar/punctuation questions. There are a few more rules about possessives, but you do not need to look at those unless you are interested.

Answer 2

Answer:

The possesive form of students is students ( a plural noun that already end with an -s)