Orbits of a particle moving in a circle are such that the perimeter of the orbit equals an integer number of de Broglie wavelengths of the particle. For a charged particle moving in a plane perpendicular to a magnetic field, the radius of the $n^{\text{th}}$ orbital will therefore be proportional to:\\
(1) $n^2$\\
(2) $n$\\
(3) $n^{1/2}$\\
(4) $n^{1/4}$