1. The problem is to simplify the radical expression $\sqrt{-10}$.\n\n2. Recall that the square root of a negative number involves the imaginary unit $i$, where $i = \sqrt{-1}$.\n\n3. We can rewrite $\sqrt{-10}$ as $\sqrt{-1 \times 10}$.\n\n4. Using the property of square roots, $\sqrt{a \times b} = \sqrt{a} \times \sqrt{b}$, we get:\n$$\sqrt{-10} = \sqrt{-1} \times \sqrt{10}$$\n\n5. Substitute $\sqrt{-1} = i$:\n$$\sqrt{-10} = i \times \sqrt{10}$$\n\n6. Since $\sqrt{10}$ cannot be simplified further (10 is $2 \times 5$, both prime), the simplest radical form is:\n$$i\sqrt{10}$$\n\nFinal answer: $\boxed{i\sqrt{10}}$