The number that is a non-integer is:

C. 2.25

An integer is a whole number that can be positive, negative, or zero, but it does not have any fractional or decimal part. Since 2.25 has a decimal part, it is not an integer.

Would you like more details or have any other questions?

Here are 5 related questions you might find interesting:

1. What is the difference between rational and irrational numbers?
2. How do you determine if a number is an integer?
3. Can a negative number be an integer?
4. What are some examples of non-integers that are rational numbers?
5. How do integers differ from whole numbers?

Tip: Always check if a number has a decimal or fractional part to determine if it is an integer.