nvm i figured it out. it was not in reference to n=4. equation used would be wavelength = 2L/n 1. The problem statement, all variables and given/known data An electron is in an infinite potential well of width L. Which is not an allowed deBroglie wavelength for the electron to have when n=4? wavelength(k) = 3L, 2L, L/2, or L/3 2. Relevant equations k=h/p would states in an infinite square well be useful too? 3. The attempt at a solution The answer I was given is 3L which is throwing me off because I thought it would be L/3. there at 2 wavelengths at n=4. 3L= 6 wavelengths which is still integer. I was thinking L/3 because 2/3 is not a valid wavelength. Was the answer i was given wrong or am I doing something wrong?