Explanation:

Let’s break this down:

- First, look at how the clusters are paired:

- I81 : K121

- D16 : F36

- O225 : ?

- Now, notice a pattern:

- In I81 : K121, 'I' is the 9th letter, 'K' is the 11th. 81 = 9², 121 = 11². So, the letter is moving from 'I' (9) to 'K' (11), which is +2, and the number goes from 81 to 121 (which is also 9² to 11²).

- D16 : F36. 'D' is 4, 'F' is 6, 16 = 4², 36 = 6². Same pattern: letter increases by +2, number is the square of letter's position.

- Now O225 : ?

- 'O' is the 15th letter. 225 = 15².

- Add +2 to 'O' (which is 15), you get 'Q' (17). 17² = 289.

- The answer has to be Q289.

Let’s look at your options:

1. Q289

2. P256

3. R324

4. P265

- The correct answer jumps right out: Q289