NCERT Books for Class 9 Science 2025-26; Download PDF (All Chapters)

Matter is anything that has mass and occupies space. Matter exists in three states: solid, liquid, and gas. 

Diffusion is the process in which particles move from high concentration to an area of lower concentration. In gases and liquids , as particles are not tightly bound with each other, they spread evenly.

In solids, particles are closely packed with each other and cannot move freely. In liquids, particles are loosely bound and can move around. In gases, particles are far apart and move freely, filling the entire space available.

Temperature and pressure affect the states of matter. As the temperature increases, the particles start moving faster and can change from solids to liquids and from liquids to gases. Increasing pressure can compress gases into liquids or solids by reducing space between particles.

Sublimation is the process by which the solid state of matter directly convert into gaseous state without first changing into liquid. Example- burning camphor which directly converts from solid to gas.

A mixture is made up of two or more substances that are physically combined and can be separated easily, like sand and salt. A compound is formed when two or more elements chemically combine with each other, like water containing hydrogen and oxygen, and cannot be separated easily.

A homogeneous mixture has the same composition throughout, like salt dissolved in water which is dissolved uniformly at all places. A heterogeneous mixture has different components that are visibly distinct, like a mixture of sand and water, where the substances remain separate.

The different methods of separating components of a mixture include filtration, distillation, evaporation, magnetic separation, and centrifugation. Each method is used for different types of mixture depending on the physical properties of the components.

Evaporation is a process that is used to separate a solid dissolved in a liquid. When the mixture is heated, the liquid evaporates, and solid remains behind. This method is commonly used to separate water from salt or sugar solutions.

A solution is a homogeneous mixture where substances are completely and uniformly dissolved. A suspension is a heterogeneous mixture where particles are not dissolved and can settle. A colloid is a mixture with smaller particles that don't settle but remain dispersed.

The laws of chemical combination include the Law of Conservation of Mass that states mass is neither created nor destroyed in a reaction, the Law of Definite Proportions means elements combine in fixed ratios, and the Law of Multiple Proportions which states that elements combine in different ratios to form different compounds.

An atom is the smallest unit of an element, that contains nucleus and electrons. A molecule is formed when two or more atoms bond together chemically, and forms the smallest unit of a compound.