#### Answer

$10i$

#### Work Step by Step

Step 1: $\sqrt (-100)$
Step 2: $\sqrt (-1\times100)$
Step 3: $\sqrt -1 \times \sqrt 100$
Step 4: Since $\sqrt -1=i$ and $\sqrt 100=10$, the expression becomes $i\times10$
Step 5: Simplifying, the final answer is $10i$