Six people, A, B, C, D, E and F, are sitting in a row,

Step 1: Position of A

“Only three people are sitting at the right of A.”

Total seats = 6
So A must be in position 3.

Positions:
1 2 3 4 5 6
_ _ A _ _ _

Step 2: Position of F

“F is sitting to the immediate right of A.”

So F is in position 4.

1 2 3 4 5 6
_ _ A F _ _

Step 3: Position of E

“E is sitting second from the extreme left.”

So E is in position 2.

1 2 3 4 5 6
_ E A F _ _

Step 4: Position of B

“F is sitting to the immediate left of B.”

So B must be in position 5.

1 2 3 4 5 6
_ E A F B _

Step 5: Position of C

“Only one person between A and C.”

From position 3, C must be position 5 or position 1.
But position 5 already has B, so C = position 1.

1 2 3 4 5 6
C E A F B _

Step 6: Remaining seat

Remaining person D goes to position 6.

Final arrangement:

1 2 3 4 5 6
C E A F B D

Answer

C is sitting at the extreme left end of the row.