Find the wrong number in the given series.
6, 12, 21, 36, 56, 81

Correct option is D

6, 12, 21, 36, 56, 81
Following pattern is followed-
6 → (+5) = 11 not 12
11→ (+10) = 21
21 → (+15) = 36
36 → (+20) = 56
56 → (+25) = 81
Therefore, correct option is (d).