To convert 10 liters to pints using the ratio of 1 liter to 2.1 pints, you can multiply the number of liters by the conversion factor:
\[ 10 \text{ liters} \times 2.1 \text{ pints/liter} = 21 \text{ pints} \]
So, 10 liters is equal to approximately 21 pints.