Three of the following four are alike in a certain way and thus form a group. Which is the one that does NOT belong to that group?

Logic: 1st + 4 = 2nd, 2nd - 2 = 3rd  

A). PUR

P + 4 = T ≠ U
U - 2 = S

B). BFD

B + 4 = F
F - 2 = D

C). VZX

V + 4 = Z
Z - 2 = X

D). JNL

J + 4 = N

N - 2 = L

So, option A is odd one out.

Thus, correct option is (a)