in 1. p to R difference is 1 and R to T difference is 1
in 2. Fto M difference is 6 nad M to k difference is 1
in 3 J to M difference is 2 nad M to p difference is 2
in 4 B to F difference is 3 nad F to J difference is 3 so we can say difference must be same in 1,3,4 for started two letter but in case of 2 it is varrying so odd one is 2 so answer is 2