Given that 'a' and 'b' are positive integers such that a + b = 10. Which of the following is the maximum possible value of a*b?

✓ Correct Answer: Option C

To maximize the product of two positive integers with a fixed sum, the numbers should be as close to each other as possible. For a + b = 10, the closest positive integers are a=5 and b=5. Their product is 5 * 5 = 25.