AP Board Class 9 Physical Science chapter 4 is basically an extension of chapter 1. However, in this unit students will further dive deeper into the concepts of pure substances and mixture and find out what pure exactly means from a chemistry perspective. Students will further be introduced to new topics like types of mixture, solution, suspension, emulsions, colloids, solvent, solute and others. The chapter also focuses on topics like;- Tyndall effect. - Separation Of Mixtures. Pure substances are substances which consist of only one type of molecule or atom. It can also be defined as substances that cannot be set apart by any of the methods of separation. A mixture is a combination of usually more than one substance. A mixture could include an element or compound which is mixed in any proportion. A homogeneous liquid mixture of two or more substances is known as a solution. It consists of a major component called the solvent and a minor component called the solute which is uniformly distributed. Any heterogeneous mixture where the materials are insoluble in a solvent and have visible particles is known as suspension. Colloids are substances having particles which are invisible to the naked eye but large molecules which are dispersed through a second substance. Gels, emulsions and sols are some of the examples of colloids. An element is a type of substance or the simplest form of matter that cannot be broken down into simpler substances by any chemical reactions. A compound is a chemically formed substance which consists of two or more types of elements bonded together in fixed proportions. Students can go through some of the chapter questions given below to gain a clearer understanding of the topics. Question 1: What is the Tyndall Effect? Answer: Tyndall effect is nothing but the scattering of a beam of light. Question 2: What do you mean by dilute and concentrated solution? Answer: If the amount of solute present is little, the solution is said to be dilute whereas if the amount of solute present is more, the solution is said to be concentrated. Stay tuned to BYJU’s to learn more about class 9 science topics and access various Andhra board study materials including syllabus, exam timetable and more.