उत्तर :
व्याख्या :

An atom is the smallest particle of a substance. Chemical substances are divided into two major groups. They are 1. Pure Substances (and) 2. Mixtures.   There are two types of pure substances that are Elements and Compounds.   Elements : An element is a substance that is made up of only one kind of atoms and cannot be broken down into simpler substances by chemical means. Metals and Non- metals come under elements. Examples of elements are Iron, Silver, Gold, Mercury etc.   Compounds : A Compound is a substance that is formed when two or more elements combine chemically. Examples of compounds are Water, Carbon dioxide, methane, vinegar etc.   Mixtures : A Mixture is formed when two or more substances mixed together but not chemically combined. Example: Air.