The 2s state of the hydrogen atom cannot decay by electric dipole radiation because a 2s → 1s transition would violate the Δl = ±1 rule (Laporte rule). In point of fact the 2s state is a metastable state with a long life time which eventually decays to the 1s state by a mechanism, such as collision with other gas molecules, which is much less probable than an electric dipole transition.
