#### Answer

$2i\sqrt 3$

#### Work Step by Step

Step 1: $\sqrt (-12)$
Step 2: $\sqrt (-1\times12)$
Step 3: $\sqrt -1\times\sqrt (12)$
Step 4: As $i=\sqrt -1$, the expression becomes $i\times\sqrt (12)$
Step 5: $i\times\sqrt (12)=i\times\sqrt (4\times3)=i\times\sqrt 4\times\sqrt 3=2i\sqrt 3$