Answer
We need $10$ 1-litre containers to hold all the soup.
Work Step by Step
We need to convert gallons into litres.
The conversion factor is $1 gal=3.79L$
Thus:
$2\frac{1}{2}gal*\frac{3.79L}{1gal}=9.45L$
We see that we need to round up to $10$ and will thus need $10$ 1-litre containers.
