A 150.0-mL sample of Solution A is diluted to a total volume of 423 mL to form Solution B. If the concentration of Solution A was originally 20.0 mg/L, what is the concentration (in mg/L) of Solution B?

20.0 mg/L A x (150.0/423) = concn B in mg/L.

Or you can use the dilution formula which is
mL1 x M1 = mL2 x M2.

To find the concentration of Solution B, we need to use the concept of dilution. Dilution is the process of adding a solvent (in this case, a liquid) to a solution to decrease its concentration.

The formula for dilution is:
C1V1 = C2V2

Where C1 is the initial concentration, V1 is the initial volume, C2 is the final concentration, and V2 is the final volume.

In this case, Solution A is diluted to form Solution B. We are given that the initial volume (V1) of Solution A is 150.0 mL, the final volume (V2) of Solution B is 423 mL, and the initial concentration (C1) of Solution A is 20.0 mg/L.

Let's substitute these values into the dilution formula:

(20.0 mg/L)(150.0 mL) = C2(423 mL)

To find C2, we rearrange the equation:

C2 = (20.0 mg/L)(150.0 mL) / (423 mL)

Now we can calculate the concentration of Solution B:

C2 = 7.09 mg/L

Therefore, the concentration of Solution B is 7.09 mg/L.