Pure Substances and Mixtures - Class VIII

Resonance involves delocalization of pi electrons through conjugated systems or empty d-orbitals where applicable. H2O has only single bonds and lone pairs, so no resonance occurs. SiO2 exists as a giant covalent network of silicon-oxygen single bonds without resonance structures. Thus, both (i) and (ii) do not exhibit resonance.

Air is a mixture of gases. $Fe + S$ is also a mixture. Bronze is an alloy and all alloys are mixtures.

Compound is made up of two or more pure substances which are always homogenous. Mixtures contains two or more pure substances physically combined which may be homogenous or heterogenous

Pure gas is not a mixture.

A compound always follow the law of constant proportions because in a compound the elements that are present are always in the constant ratio.

Compounds are pure substances whereas mixture are impure substances. The constituents of a compound can be separated only by chemical methods and that of a mixture can be separated easily by physical methods. The constituents of a compound are present in a fixed ratio.The constituents of a mixture are present in varying ratios.

Compound is made up of two or more elements that are chemically combined whereas mixtures are made up of two or more pure substances that are physically combined. 

Mixtures can be homogeneous or heterogeneous. Oil and Water is a heterogeneous mixture.

Electrolysis decomposes the water into oxygen and hydrogen due to passage of electric current.

Matter that consists of two or more substances which may be elements, compounds or both mixed together physically in any proportion, but not chemically combined is called as a mixture. Each component of a mixture retains its individual properties. 

Brass, Air and Bitumen are all mixtures. None of them are compounds.

A mixture consists of two or more substances which may be elements, compounds or both mixed together physically in any proportion, but not chemically combined. However, a compound consists of two or more elements that are chemically combined in a fixed proportion. Hence, a compound is different from a mixture.

The components present in the mixture are in variable proportions.

The parts of a mixture can be separated by physical means. A mixture does not have a sharp melting or boiling point. It may be homogeneous or heterogeneous. Energy is neither given out nor absorbed in the preparation of a mixture. However, heat is taken in or given out in the preparation of a compound.

All the compounds are made up of different elements and have properties different from their constituent element.

Mixture and a compound both follow the law of conservation of mass so their weight equals to the sum of mass of their components.

Ionic compounds consist of strong electrostatic forces between ions, requiring high energy to break, resulting in high melting and boiling points. Covalent compounds consist of molecules held by weaker intermolecular forces, resulting in lower melting and boiling points.

A mixture or a compound can give further simplification using ordinary means.

A commercial cake is a mixture of compounds. 

$\text{Distillation is a way of seperation substances based on the difference in their boiling points}$

Isotropic medium is the one in which permeability and permittivity are unifrom in all directions,

Air is a mixture of gases, not a pure substance like an element or a compound.

The components of compounds can be separated by chemical means. Rest all are properties of compounds.

The components in compounds do not retain their original properties.

The components in mixtures retain their original properties.