Question

If i change the concentration of the 3% hydrogen peroxide solution to 1.5%, am I changing its concentration or percent concentration?

Answer 1

both. The 3% is 3g/100 mL (w/v) and the 1.5% is only 1.5g/100 mL so you have changed the concentration. Obviously there is less H2O2/100 mL in the 1.5% solution. But you have changed the percent too. Obviously, from 3% to 1.5%.