The normal freezing point of water is 0oC and it's freezing point depression constant is 1.86oC/m. If a 2.00 molal solution of Na2SO4 is prepared, what is the freezing point of the mixture?

Consider hydrogen in an excited state n = 5n=5 that emits photons to reach the ground state. there are various possible transitions other than straight to the ground state that can occur; for example, it can drop to the n = 3n=3 state followed by the n = 3n=3 to the ground state transition. which of the possible transitions will result in the emission of a photon in the visible region?