Correct answer is :: P - 1, Q - 4, R - 2, S - 3
Explanation::
SMTP is application layer protocol but take help of TCP for activation over link for transfering mail.
TCP:: It is transport layer protocol.
BGP:: Border Gateway procoly is used to connect two AS and used in Network layer.
While PPP:: Point to point connection with the help of MAC will come under the category of Data Link layer.