"it" "one" and "them"

[nyugaton]

(1) If you see any interesting book, buy it for me.

(2) If you see any interesting book, buy one for me.

(3) If you see any interesting books, buy one for me.[correct]

(4) If you see any interesting books, buy some for me.[correct]

(5) If you see any interesting books, buy them for me.

I think (3) and (4) are without question correct. What about the rest?

[JMB1122]

(1) If you see any interesting book, buy it for me.
(2) If you see any interesting book, buy one for me.
(3) If you see any interesting books, buy one for me.[correct]
(4) If you see any interesting books, buy some for me.[correct]
(5) If you see any interesting books, buy them for me.
I think (3) and (4) are without question correct. What about the rest?

(1) If you see an interesting book, buy it for me. (corrected)

(2) Incorrect

Number five is correct; however, you are telling the person to buy all of the interesting books that they see. (depending on their definition of interesting, you may end up with a lot of books