Hello. I have found an exercise that reads: "The wave function of a one-electron atom is: [1s orbital, atom: Li2+ What will be the most likely distance to locate the electron?" Solution of exercise is: My question is: Why the square of the probability density is dP/dV, and therefore the volume formula is used? I had always done this exercise by the square of the wave function, deriving the function and finding the maximum... I don't know why it's used the volume of a sphere here... Thank you!