You can have a solution of hydrogen peroxide that might say 10% that means that 10% per mass of the hydrogen peroxide solution is the hydrogen peroxide the rest is water.
concentration is the amount of mass in the solution eg 5gdm-3
hope that helps
Squeezing just the juices out of the orange, like with your hand or whatever you use, is a physical change. yes :)
The name come from the German 'Bisemutum' a corruption of 'Weisse Masse' meaning white mass.