Which element can form basic compunds

Can someone me with questions 15 to 17 plz.

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.)

This classification of drug typically changes the brain's chemistry and reduces its ability to create its own endorphins.