In Choose odd Number questions, certain numbers are given, out of which all except one are alike in some manner while one is different and this number is to be chosen as the answer.

Choose or find odd number

21 , 69 , 81 , 83

A. 21
B. 69
C. 81
D. 83
Answer: C . 81

Justification: 81 is the only square number in the group.