#### Answer

$2i$

#### Work Step by Step

Step 1: $(1+i)^{2}$
Step 2: $(1+i)(1+i)$
Step 3: $1(1+i)+i(1+i)$
Step 4: $1+i+i+i^{2}$
Step 5: As $i^{2}=-1$, the expression becomes $1+2i-1$
Step 6: $1+2i-1=2i$
Step 7: Therefore, the rectangular form of the expression is $2i$.