Answer:
206 mL
Step-by-step explanation:
In the annexed picture you can see your same question, just in another format.
First we calculate the total moles of CuF₂ that are required in the working solution:
1967 μM ⇒ 1967 / 10⁶ = 1.967 x10⁻³M
1.967 x10⁻³M * 0.275 L = 5.409x10⁻⁴ mol
Now we divide those moles by the concentration of the stock solution, to calculate the volume:
5.409x10⁻⁴ mol ⇒ 5.409x10⁻⁴ * 1000 = 0.5409 mmol
0.5409 mmol ÷ (2.63 mmol/L) = 0.206 L
0.206 L ⇒ 0.206 * 1000 = 206 mL