What is the smallest number that can be formed using the digits 8, 3, 5, 7 and 2 exactly once?

The correct option is D 23578
When we use all the given digits exactly once, we get a five-digit number.

To form the smallest 5-digit number from them, we place the largest of the digits at a place with the lowest place value.

Thus, 8 will be in the ones place.

Next, we place the second highest digit in the next highest place. That is, 7 in the tens place.

We continue the process till all the digits are placed.

$\begin{array}{ccccc}\text{Ten thousands}& \text{Thousands}& \text{Hundreds}& \text{Tens}& \text{Ones}\\ 2& 3& 5& 7& 8\end{array}$

Thus, the required number is 23578.