Achange in color, such as rusting of metal, is a sign that

Iron undergoes a chemical reaction called oxidation to form rust, or iron oxide. ... Copper forms a turquoise colored oxide and silver forms a black oxide. In both cases you know that a chemical reaction has taken place because of the color change.

adding or remove a gaseous reactant or product changes the concentrations. if the concentration of reactant or product is increased, the system will shift away from the side in which concentration was increased (i.e. if the concentration of reactants is increased, the system will shift toward the products. if more products are added, the system will shift to form more reactants). conversely, if the concentration of reactant or product is decreased, the system will shift toward the side in which concentration was decreased (i.e. if reactants are removed, the system will shift to form more reactants. if the concentration of products is decreased, the equilibrium will shift toward the products).

explanation:

d. temperate deciduous forest