Is ammonia a compound element or mixture

The rules of engagement (roe) working group is often used to (select all that apply.)

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?

What is the empirical formula of a compound that is 50.7% antimony and 49.3% selenium ?