Starting from J, if all all the persons are made to sit in the alphabetical order in clockwise direction, the positions of how many (excluding J) will remain unchanged?

P is third to the left of M and O is second to the left of P. 28 year old is neighbour of both O and P, => 28 year old sit between O and P.

Only one person sits between M and L, => Let he sits second to the left of M.

K is third to the left of 28 years old, => K sits to the immediate right of M.

Q is second to the right of J and J is not 28 years old, => Q is 28 years old and sits between O and P, while J sits between O and K.

Now, the only vacant spot, i.e. to the immediate left of M is taken by N.

39 year old is second to the left of N, => P is 39 years old.

13 year old is second to the right of K, => O is 13 years old. Also, M is 16 year old.

K is elder to N but younger than L, => L > K > N 

16 year old and 9 year old are not immediate neighbours, => From above statement L can't be 9 years old, hence J is 9 years old.

Starting from J, if all all the persons are made to sit in the alphabetical order in clockwise direction, the position of only K will remain unchanged.

=> Ans - (B)