The correct answer to this question is C, 25. To answer this question, one would need to know the primary sequence of numbers. One would have to be at least able to count to 26. Knowing the series of numbers, they would know that 25 is the number after 24, but before 26.
This makes 25 the correct number that is missing between 24 and 26. This type of question would be found on a math test, where it is necessary to know numbers. It could also be found on a reading comprehension test to ensure the student can read the numbers.