Identify any two statements that are true for pure substances among the following: (I) Pure substances contain only one kind of particles. (II) Pure substances may be compounds or mixtures. (III) Pure substances have the same composition throughout. (IV) Pure substances can be exemplified by all elements other than nickel.

Mrs. Johnson, a high school chemistry teacher, explains the difference between pure substances and mixtures to her class. She tells pure substances and mixtures are two fundamental categories of matter. Pure substances have a uniform and definite composition, consisting of only one type of particle. They can be further classified into elements and compounds. She demonstrates with water (H₂O) and sodium chloride (NaCl), highlighting that compounds have a uniform and definite composition. She shows copper (Cu) as an example of an element, which cannot be broken down into simpler substances. Moving to mixtures, she uses saltwater to illustrate how mixtures consist of two or more substances physically combined, allowing for variable compositions. She then engages students in creating their own mixtures and discussing separation techniques like filtration and evaporation.

CASE_STUDIESPure and Impure Substances in ChemistryDefinition of Mixture in ChemistryDefinition and Properties of Colloids