How many persons sit between K and L, when counted from the left of K ?

M sits second to the left of Q. There are 2 persons in between Q and L. L sits to the right of Q (second last statement).

From these statements, we can infer the following diagram.

Let us number the positions starting from 1 to make things easier.

3 persons sit between L and M's sister. M's son sits second to the right of M's sister.

M's sister can be at positions 10 or 2. Let us assume the position of M's sister to be 2 and proceed. If this assumption fails, we will reconstruct the diagram with M's sister at 10.

Now, only 1 person sits between M's son and S. Now, M's sister can be S or L.

Also, it is given that there are 4 persons between M's Father and M. Therefore, L must be M's Father. S must be M's sister

S is an immediate neighbour of M's mother. Hence, M's mother must be Q. Only 3 persons sit between M's mother and M's brother. Person at 7 or 9 can be M's brother.

Let us assume the person at position 9 to be M's brother.

J sits to the immediate right of R. R is neither the son nor the mother of M. J can sit at position 10 and R at position 9. M's daughter sits second to the left of M's brother. M's daughter sits at position 7. M's wife sits third to the right of K. Let us assume K to be M's daughter. This implies that J will be M's wife.

The final arrangement is as follows.

Any other assumption leads to clash of the facts given at one point of time or another. All the questions can be answered using the diagram given above.

No person sits between K and L. Hence, option C is the right answer.