Is steel a mixture or pure substance?

Which of the following elements would you expect to have the lowest ionization energy value? fluorine, lithium, neon, nitrogen

Why is carbon ideal for making different compounds?

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?