An electron in a hydrogen atom moves in a circular orbit of radius \(r\) in a stationary state characterized by the principal quantum number \(n\). The electron's orbital angular momentum is quantized according to \(L = \dfrac{n h}{2\pi}\), where \(h\) is Planck's constant. Which of the following expressions correctly represents the electron's de Broglie wavelength \(\lambda\) in terms of \(r\) and \(n\)?