Odd Man Out

All other groups consist of alternate letters.

In all other groups, first and third letters as well as second and fourth letters are consecutive.

All except Chicken can live in water.

In all other pairs, the two words are antonyms of each other.

681 is odd number as 10, 12, 234, 681, 99710 = 1 + 0 = (1)² 13 = 1 + 3 = 4 = (2)² 234 = 2 + 3 + 4 = 9 = (3)2 997 = 9 + 9 + 7 = 25 = (5)² 681 = 6 + 8 + 1 = 15 ≠ (4)²

The first and third letters are alternate letters in all except option B.

This is the only group which has no vowel.

The pair 104 and 78 is different from others as all others are divisible by 4.

In all other groups contain two alternate letters in reverse order.

83 is the only prime number in the group.