1. The problem is to find the square root of $-0.021$. 2. Recall that the square root of a negative number is not a real number, but an imaginary number. We use the imaginary unit $i$ where $i^2 = -1$. 3. To find $\sqrt{-0.021}$, rewrite it as $\sqrt{-1 \times 0.021} = \sqrt{-1} \times \sqrt{0.021} = i \times \sqrt{0.021}$. 4. Calculate $\sqrt{0.021}$. Since $0.021$ is positive, its square root is a real number approximately $0.1449$. 5. Therefore, $\sqrt{-0.021} = i \times 0.1449 = 0.1449i$. Final answer: $$\sqrt{-0.021} = 0.1449i$$