Facing: North
1) Q is sitting second from on the extreme ends.
(Here two cases are possible Case I Q is sitting second from the extreme North end Case II where Q is sitting second from the extreme south end)
2) Only two people are sitting between Q and
3) S is sitting seventh to the right of M.
Here Case II eliminates as Q is sitting second from the extreme end so S will not sit beyond.
4) L is sitting exactly in between Q and S.
5) Only one person is sitting between S and O.
(As O can sit both the sides of S. So, In Case I.I O is sitting second to the right of S and in Case I.II O is sitting second to the left of S.)
6) O is sitting third to the left of R.
7) R is not an immediate neighbour of S.
Here Case I.II eliminates as R is not an immediate neighbour of S.
8) P is sitting second to the left of N, who is sitting fourth to the right of R.
The final arrangement
So, 21 people are sitting in the row.
We always count the number of person whether they are defined or not in the final arrangement so here we will count all the seats as these are for the persons.