To determine the amount of pure acid in the 120 liters of a 75 percent acid solution, we can use the following formula:

Amount of pure acid = (Percentage of acid / 100) * Total volume of solution

In this case, the percentage of acid is 75%, and the total volume of the solution is 120 liters. Plugging these values into the formula, we get:

Amount of pure acid = (75 / 100) * 120 liters

Amount of pure acid = 0.75 * 120 liters

Amount of pure acid = 90 liters

Therefore, there are 90 liters of pure acid in the 120 liters of 75 percent acid solution.