Which of the following is not a possible de-Broglie's wavelength of a particle, which moves inside a cubical box of side length L, without losing any energy (elastically colliding with walls of cube)?

Using concept of stationary waves, we can say at rigid walls Node formation takes place.L=λ2, λ, 3λ2, 2λ..., nλ2 where n=1,2,3... Longest wavelength is specified by λ=2L. next by λ=Lthen λ=L×23. etc  In general λn=2Ln,n=1,2,3,…For(a) λ=2L3For (b) λ=LFor (c) )λ=2L . Hence, all are possible.