I have 0.500ml of 3M ethanol and then I take 0.250ml of it and put it to 0.250ml of 0.06M phosphate buffer, what is the final concentration?

Answer 1

of what? the ethanol? The final concn of the ethanol, assuming volumes are additive, is
3M x [0.250 mL/(0.250+0.250)] = 1.5M
right?
(Note: ethanol and water volumes are not additive. Approximately 4% error).