How can you separate a mixture of dry materials

In which layer of earth do most earthauakes occur a_ inner core b_outer core c_mantle d_crust

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.)

How are the terms group and period used on the periodic table