Four of the following five are alike in a certain way and thus form a group. Find the one which doesn’t belong to the group? Study the following information carefully and answer the questions given below:
Seven persons -M, N, O, P, Q, R and S sit in a linear row and facing the north but not necessarily in the same order.
Only four persons sit between P and Q who does not sit at the extreme end of the row. S sits to the immediate right of Q. The number of persons sitting to the right of S is same as the number of persons sitting between M and N who sits to the immediate left of R. O sits to the left of R.

To determine which person does not belong to the group, we must first analyze the seating arrangement based on the given clues.

Let the 7 positions in the row from left to right be represented by indices 1 to 7. All persons face north.

Step 1: Analyze the positions of P and Q.
We are told: "Only four persons sit between P and Q who does not sit at the extreme end of the row."
Since there are 4 persons between P and Q, the distance between their positions is 5 (i.e., if one is at position $x$, the other is at $x+5$).
The possible pairs of positions for {P, Q} in a 7-person row are:
- Case A: Position 1 and Position 6
- Case B: Position 2 and Position 7
Since Q does not sit at the extreme end of the row, Q cannot be at position 1 or 7.
Therefore:
- From Case A: Q must be at position 6, and P must be at position 1.
- From Case B: Q must be at position 2, and P must be at position 7.

Step 2: Place S.
We are told: "S sits to the immediate right of Q."
- If Q is at position 6 (Case A), S must be at position 7. This is a valid configuration.
- If Q is at position 2 (Case B), S must be at position 3. This is also a valid configuration.

Step 3: Analyze the positions of M, N, R, and O.
Let us evaluate each remaining case:

Case 1: Q is at 6, P is at 1, S is at 7.
The arrangement so far is:
Row: [P, _, _, _, _, Q, S]
Positions: 1: P, 2: _, 3: _, 4: _, 5: _, 6: Q, 7: S.
Now let's look at the clue: "The number of persons sitting to the right of S is same as the number of persons sitting between M and N who sits to the immediate left of R. O sits to the left of R."
- The number of persons sitting to the right of S (position 7) is 0.
- Therefore, the number of persons sitting between M and N must be 0. This means M and N sit adjacent to each other.
- We are given: "N sits to the immediate left of R". This means the sequence of N and R is: NR.
- Since M and N are adjacent, M can be either to the left of N (giving MN) or to the right of N. But R is immediately to the right of N, so M must be to the immediate left of N. Thus, we have the contiguous block: M N R.
- The vacant positions available for this block of 3 are positions 2, 3, 4, and 5.
- If MNR occupies 2, 3, 4:
- 2: M, 3: N, 4: R. - The remaining positions are 5. O must sit at position 5. - However, we are told: "O sits to the left of R." Here, O is at 5 and R is at 4, so O is to the right of R. This is invalid.
- If MNR occupies 3, 4, 5:
- 3: M, 4: N, 5: R. - The remaining position is 2. O must sit at position 2. - Here, O (at 2) sits to the left of R (at 5). This is valid! - The final arrangement for Case 1 is:
1: P, 2: O, 3: M, 4: N, 5: R, 6: Q, 7: S.

Case 2: Q is at 2, P is at 7, S is at 3.
The arrangement so far is:
Row: [_, Q, S, _, _, _, P]
Positions: 1: _, 2: Q, 3: S, 4: _, 5: _, 6: _, 7: P.
- The number of persons sitting to the right of S (position 3) is 4 (positions 4, 5, 6, 7).
- Therefore, the number of persons sitting between M and N must be 4.
- The available vacant positions for M and N are among 1, 4, 5, 6. The only pair of positions that has exactly 4 positions between them in a 7-person row is 1 and 6 (which has 2, 3, 4, 5 between them). But position 2 and 3 are occupied by Q and S, and 7 is occupied by P.
- Let's check: if one of M/N is at 1, and the other is at 6, the number of positions between them is 4 (positions 2, 3, 4, 5). This matches!
- Since N sits to the immediate left of R, R must be at position 7 if N is at 6. But position 7 is occupied by P. Thus, N cannot be at 6.
- If N is at 1, R must be at 2. But position 2 is occupied by Q. Thus, N cannot be at 1.
- Therefore, Case 2 is invalid.

Final Seating Arrangement:
From left to right: P - O - M - N - R - Q - S

Now, let's analyze the options: M, O, Q, S to find the one that doesn't belong to the group.
Let's check the positions of these persons in the row:
- P is at position 1 (Extreme Left End)
- O is at position 2
- M is at position 3
- N is at position 4
- R is at position 5
- Q is at position 6
- S is at position 7 (Extreme Right End)
Comparing the options:
- M is at an odd-numbered position (3).
- O is at an even-numbered position (2).
- Q is at an even-numbered position (6).
- S is at an odd-numbered position (7).
Alternatively, let us look at their neighbors:
- M is sitting between O and N (middle seat).
- O is sitting between P and M (middle seat).
- Q is sitting between R and S (middle seat).
- S is sitting at the extreme right end of the row (has only one neighbor, Q).
Since S sits at the extreme end of the row, while M, O, and Q sit in the middle of the row, S does not belong to the group.

Therefore, the correct option is S.