Chemical reaction takes place when iron is added copper sulphate solution but no reaction takes place when copper dust is added into ferrous sulphate solution .Why?Describe in brief the effect of physical state of reactants in chemical reaction.​

Consider a culture medium on which only gram-positive organisms such as staphylococcus aureus colonies can grow due to an elevated nacl level. a yellow halo surrounds the growth, indicating the bacterium fermented a sugar in the medium, decreasing the ph as a result and changing the color of a ph indicator chemical. this type of medium would be referred to as a differential and enrichment culture.