Correct option is B
The place values of the letter clusters based on their positions in the alphabet and determine the odd one by adding their respective place values:

DF: Sum = 4 + 6 = 10
BO: Sum = 2 + 15 = 17
CG: Sum = 3 + 7 = 10
AI: Sum = 1 + 9 = 10
Conclusion:
DF = 10
BO = 17
CG = 10
AI = 10
The odd one out is BO, as its sum (17) is different from the others, which all sum to 10.
Correct answer is (b) BO.