How many particles would be found in a 12.7 g sample of ammonium carbonate?

What does the symbol (–hfus) indicate in a phase change?

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?

Ab c or d ? i’m not sure what the answer is