Why is balancing a chemical equation necessary?

Write the balanced chemical equation of the reaction.
Sodium chloride  $+$  Manganese dioxide  $+$ Sulphuric acid$\to$Sodium hydrogen sulphate$+$Manganese sulphate $+$ Water $+$Chlorine

Consider the following statements.

I. A chemical equation tells us about the substances involved in a reaction.

II. It gives information about the symbols and formula of substances involved in a reaction.

III. It tells us about the atoms or molecules of the reactants and products involved in a reaction.

The correct statement(s) is/are

Write the equation and balance them.

Silver oxide+Hydrogen peroxide$\to$Silver+Water+Oxygen

What information does the following chemical equation convey:

$\mathrm{Zn}+{\mathrm{H}}_2{\mathrm{SO}}_4\to {\mathrm{ZnSO}}_4+{\mathrm{H}}_2$

Consider the following equations.

$\mathrm{Pb}\left({\mathrm{NO}}_3{)}_2\right(\mathrm{aq}) +2\mathrm{KI} (\mathrm{aq}) \to {\mathrm{Pbl}}_2(\mathrm{w}) +2{\mathrm{KNO}}_3$(x)

$\mathrm{Zn}\left(\mathrm{y}\right) +{\mathrm{H}}_2{\mathrm{SO}}_4\left(\mathrm{aq}\right) \to {\mathrm{ZnSO}}_4\left(\mathrm{aq}\right) +{\mathrm{H}}_2\left(\mathrm{z}\right)$

What are w, x, y and z in the above equations?

The chemical reaction, 

${\left({\mathrm{NH}}_4\right)}_2{\mathrm{Cr}}_2{\mathrm{O}}_7\stackrel{∆}{\to }{\mathrm{N}}_2+4{\mathrm{H}}_2\mathrm{O}+{\mathrm{Cr}}_2{\mathrm{O}}_3$ is an example of 

Balance the following chemical equation.
$\mathrm{C}+{\mathrm{HNO}}_3\to {\mathrm{CO}}_2+{\mathrm{H}}_2\mathrm{O}+{\mathrm{NO}}_2$

Sodium chloride reacts with silver nitrate to produce silver chloride and sodium nitrate.
(i) Write the chemical equation.
(ii) Check whether it is balanced, if not then balance it.
(iii) Calculate weight of reactant and product. 
(iv) Write the law which this chemical equation satisfies.

What information does the following chemical equation convey:

$\mathrm{Mg}+2\mathrm{HCI}\to {\mathrm{MgCI}}_2+{\mathrm{H}}_2$