Answer
$1~L$ is greater by $0.01~L$.
Work Step by Step
First, we convert 990 mL to Liters:
$990~ml*\frac{1~L}{1000~mL}=0.99~L$
This is clearly less than $1~L$. We find the difference:
$1~L-0.99~L=0.01~L$
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