Explanation:

- Option 1: 25 : 16 : 9

- These are all perfect squares: 5², 4², 3².

- Option 2: 64 : 100 : 18

- 64 and 100 are perfect squares (8², 10²), while 18 is not.

- Option 3: 81 : 9 : 19

- 81 is a perfect square (9²), and 9 is a perfect square (3²), but 19 is not a perfect square.

- Option 4: 16 : 64 : 12

- These are perfect squares (4², 8²) and 12 is not.

The odd one out is Option 2 because it includes two perfect squares but the third number is not. All other options have one or two perfect squares with a clear pattern or comparison.