Others are natural geographical features.

Cool

Except (d), remaining are synonyms.

Remaining numbers are composite.

1 2 3 4 5 6
A B C D E F
D = 4, W = 4 (from backward count)
F = 6, U = 6 (From backward)
Similarly, K = 11, Q = 10

104 :78 = 104/26 : 78/26
=4 : 3
64 : 48 = 64/16 : 48/16
= 4 :3
80 : 60 = 80/20 : 60/20
= 4 : 3
But, 96 :80 = 96/16 : 80/16
= 6 : 5
The odd is 96 : 80 because its ratio is 6 : 5 but rest of ratio is 4 : 3.

Except 44 - 31, the difference of the remaining pairs are perfect squares.

Except option (b) rest all has vowel

Except option (c) all are number i.e.,
EIGHT → GHIET; VEENS → SEVEN etc.

8(3 + 5) -------- 15(3 x 5)
25 = (5)² ----------- 36 = (6)²
49 = (7)² ------------ 64 = (8)²
81 = (9)² ----------- 100 = (10)²