The concentration of a solution made by diluting 10.0 mL of 0.685 mol/L NaBr to 300 mL is

0.685 mol/L x (10/300) = ?

To find the concentration of the final solution, we can use the formula for dilution:

C1V1 = C2V2

Where:
C1 = Initial concentration
V1 = Initial volume
C2 = Final concentration
V2 = Final volume

In this case, the initial concentration (C1) is 0.685 mol/L, and the initial volume (V1) is 10.0 mL. The final volume (V2) is given as 300 mL.

To find the final concentration (C2), we rearrange the formula:

C2 = (C1V1) / V2

Plugging in the values:

C2 = (0.685 mol/L * 10.0 mL) / 300 mL

First, we need to convert mL to L:

C2 = (0.685 mol/L * 0.010 L) / 0.300 L

Calculating:

C2 = 0.0228 mol/L

Therefore, the concentration of the solution made by diluting 10.0 mL of 0.685 mol/L NaBr to 300 mL is 0.0228 mol/L.