Which are geologic evidence?

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

Silver tarnishes as silver metal reacts with hydrogen sulfide, h2s, in the air. in this reaction, dark silver sulfide, au2s, covers the surface of silver. when silver is polished, this coating of silver sulfide can be removed from the surface. this makes the silver shiny again. enter the coefficients that balance the tarnishing reaction equation. (type 1 for no coefficient.)

Why does his teacher ask him to balance the equation by including the correct coefficient