Explanation:
We are given a group of numbers: B4, E25, D16, I91, and F36. We need to identify the number that does not belong to this group.

To solve this problem, we can look for a pattern or similarity among the numbers in the group.

- B4: The letter B does not have any significant meaning in this context and can be ignored. The number 4 is a perfect square (2^2 = 4).
- E25: The letter E does not have any significant meaning in this context and can be ignored. The number 25 is a perfect square (5^2 = 25).
- D16: The letter D does not have any significant meaning in this context and can be ignored. The number 16 is a perfect square (4^2 = 16).
- I91: The letter I does not have any significant meaning in this context and can be ignored. The number 91 does not have any obvious pattern or similarity with the other numbers in the group.
- F36: The letter F does not have any significant meaning in this context and can be ignored. The number 36 is a perfect square (6^2 = 36).

Based on the analysis above, we can see that all the numbers in the group are either perfect squares or do not have any obvious pattern. However, the number 91 stands out as it does not have any clear connection or similarity with the other numbers. Therefore, the number I91 does not belong to this group.

Conclusion:
The number I91 does not belong to the group because it does not have any clear connection or similarity with the other numbers.