Here's how to calculate the number of lactic acid molecules in the solution:

1. Moles of Lactic Acid:

* Molarity (M) = moles of solute / liters of solution

* We have a 0.5 M solution and 1 L of solution.

* Rearranging the formula: moles of solute = Molarity * liters of solution = 0.5 M * 1 L = 0.5 moles

2. Number of Molecules:

* Avogadro's number (N_A) = 6.022 x 10^23 molecules/mole

* Number of molecules = moles * Avogadro's number

* Number of molecules = 0.5 moles * 6.022 x 10^23 molecules/mole = 3.011 x 10^23 molecules

Therefore, there are approximately 3.011 x 10^23 molecules of lactic acid in 1 L of a 0.5 M solution.