An element is a pure substance which consists of only one type of particles.these particles can be atoms or molecules.for example , carbon is only made up of carbon atoms or hydrogen gas is made up of hydrogen molecules.
an expression which gives the no: and type of atoms present in a moleculeof a substance.for example .there are 6 C and  14 H in a hexane molecule.

acids are substances having a sour taste.the word acid comes from a latin word acere meaning sour.acids are corrosive and react with bases to form salt and water. also , acids turn blue litmus paper red.for example , HCl , sulphuric acid.

bases are defined as chemical substances that are bitter to taste and soapy to touch.they react with acids to form salts and turns red litmus paper blue. for example , sodium hydroxide , potassium hydroxide.

salt is defined as the product formed along with water when an acid reacts with base.this reaction is termed as neutralization reaction. for example , 
 NH3 + HCl → NH4Cl
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