Identify which of the following statements are TRUE. The composition of a pure substance is variable.
The density of a pure substance is fixed.
The properties of mixtures are constant and fixed.
The component part of mixtures cannot be separated by any method.

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.