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To express the measurement of any physical quantity two things are considered: (i) Its unit, (ii) The numerical value. Magnitude of a physical quantity = numerical value * unit Units are of two types: (i) Basic units (ii) Derived units (i) The basic or fundamental units are those of length (m), ass (kg), time (s), electric current (A), thermodynamic temperature (K), amount of substance (mol) and luminous intensity (cd). (ii) Derived units are basically derived from the fundamental units, e.g., unit of density is derived from units of mass and volume. The systems used for describing measurements of various physical quantities are (a) CGS system: It is based on centimetre, gram and second as the units of length, mass and time respectively. (b) FPS system: A British system which used foot(ft). pound (lb) and second (s) as the fundamental units of length, mass and time. (c) MRS system: Uses metre (m), kilogram (kg) and second (s) respectively for length, mass and time; ampere (A) was added

Atom is the smallest particle of an element which can take part in a chemical reaction. It mayor may not be capable of independent existence. Molecule is the simplest particle of matter that has independent existence. It may be homoatomic e.g., H₂, CI₂, N₂ (diatomic), O3(triatomic) or heteroatomic, e.g., HCI, NH₃, CH₃ etc

Compound          It is also the form of matter which can be formed by combining two or more elements in a definite ratio by mass. It can be decomposed into its constituent elements by suitable chemical methods, e.g., water (H₂O) is made of hydrogen and oxygen in the ratio 1 : 8 by mass. Compounds can be of two types : (i) Inorganic compounds: Previously, it was believed that these compounds are derived from non-living sources, like rocks and minerals. But these are infact the compounds of all the elements except hydrides of carbon (hydrocarbons) and their derivatives. (ii) Organic compounds: According to earlier scientists, these compounds are derived from living sources like plants and animals, or these remain buried under the earth (e.g., petroleum). According to modern concept, these are the hydrides of carbon and their derivatives. Mixture        These are made up of two or more pure substances. They can possess variable composition and can be separated into their components by so

Element        It is the simplest form of pure substance, which can neither be decomposed into nor built from simpler substances by ordinary physical and chemical methods. It contains only one kind of atoms. The number of elements known till date is 118. [Hydrogen is the most abundant element in the universe. Oxygen (46.6%), a non-metal, is the most abundant element in the earth crust. Aluminium is the most abundant metal in the earth crust. An element can be a metal, a non-metal or a metalloid.]

MATTER           Anything which occupies some space and have some mass is called matter. It 15 made up of small particles which have space between them. The matter particles attract each other and are in a state of continuous monon. STATES       SOLID: Solid-state is nothing but one of the states of matter.they have the ability to resist any force that is applied to its surface. However, the solid-state of compounds largely depends on the properties of atoms such as their arrangement and the forces acting between them.       LIQUED: A liquid is a almost incompressible fluid that conforms to the form of its field however keeps a ( almost ) regular extent unbiased of pressure. As such, it's miles one of the 4 essential states of matter (the others being solid, gas, and plasma), and is the handiest kingdom with a specific extent however no constant form .       GAS: Gas is a situation that doesn't have a set form and a set size. Gasses have decre