To find the mean proportional between two numbers, we need to use the concept of geometric mean. The mean proportional (also known as the geometric mean) between two numbers a and b is the square root of their product. Mathematically, the mean proportional x can be represented as:

x = \sqrt{a \times b}

For this question, we are given the numbers 28 and 252. Let's calculate the mean proportional:

x = \sqrt{28 \times 252}

First, let's calculate the product:

28 \times 252 = 7056

Now, take the square root of 7056:

x = \sqrt{7056}

By calculating the square root:

\sqrt{7056} = 84

Therefore, the mean proportional between 28 and 252 is 84.

Conclusion: The correct answer is 84.