To calculate the number of liters of hydrochloric acid in a 300-liter solution that is 10% hydrochloric acid, we can use the following formula:

Volume of Hydrochloric Acid = Total Volume of Solution × Percentage of Hydrochloric Acid

Let's substitute the given values into the formula:

Volume of Hydrochloric Acid = 300 liters × 10%

Volume of Hydrochloric Acid = 300 liters × 0.10

Volume of Hydrochloric Acid = 30 liters

Therefore, there are 30 liters of hydrochloric acid contained in the 300-liter solution that is 10% hydrochloric acid.