Solution:The pattern followed here is :
{1st letter + 4 = 2nd letter}, {2nd letter + 3 = 3rd letter}, {3rd letter + 4 = 4th letter} & {4th letter + 3 = 5th letter}
MQTXA → (M + 4 = Q), (Q + 3 = T), (T + 4 = X) & (X + 3 = A)
SWZDG → (S + 4 = W), (W + 3 = Z), (Z + 4 = D) & (D + 3 = G)
JNQUX → (J + 4 = N), (N + 3 = Q), (Q + 4 = U) & (U + 3 = X)
But,
PTXBF → (P + 4 = T), (T + 3 ≠ X), (X + 4 = B) & (B + 3 ≠ F)
Hence, PTXBF is the correct answer.