Which of the following can be formed by physically combining pure substances?
a. an element
c. a compound
b. a mixture
d. all of the above

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.)

8) warming your hands by a fire is an example if which heat transfer? a. conduction b. convection c. radiation d. none of these

In the reaction h2co3 (aq) + 3nh3 (aq) = 2 nh4+ (aq) + co3 2-, how many electrons are transferred?