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To determine how much of a 50% solution of boric acid is needed to make 1 L of a 10% solution, we can apply the concept of dilution and solution concentration.

We start with the formula that relates the concentrations and volumes of the solutions involved. The formula to use is:

C1V1 = C2V2

Where:

- C1 is the concentration of the stock solution (50% in this case),

- V1 is the volume of the stock solution needed,

- C2 is the concentration of the desired solution (10%),

- V2 is the final volume of the desired solution (1 L or 1000 mL).

Setting up the equation:

(50%)(V1) = (10%)(1000 mL)

To find V1 (the volume of the 50% solution), we can rearrange the equation:

V1 = (10% * 1000 mL) / 50%

Calculating this gives:

V1 = (10000/50) mL = 200 mL

This indicates that 200 mL of the 50% solution is required to achieve a final concentration of 10% in 1 liter of solution