Look for the largest square factor of 250. Since 250 = 25 × 10 and √25 = 5, we get √250 = 5√10. To simplify a surd, split the number under the root into a perfect-square factor and the remaining factor. Take the square root of the perfect square outside the radical. The expression is simplified when no square factor greater than 1 remains under the root. The correct answer is 5√10, which matches the calculation or reasoning shown.