Chemical Equations

A molecule of an element or a compound is represented by its _____. (Valency/ formula)

What are compound radicals? Give examples of a few radicals, along with their valences. Also mention some compounds containing compound radicals. Give the valencies of the parts that make up the compound.

Find the valences of the underlined elements or radicals in the following compounds.
$\underset{\_}{\mathrm{B}\mathrm{a}}\mathrm{C}{\mathrm{l}}_2,\underset{\_}{ \mathrm{P}}\mathrm{C}{\mathrm{l}}_3, \underset{\_}{\mathrm{P}}\mathrm{C}{\mathrm{l}}_5, \underset{\_}{\mathrm{N}}{\mathrm{H}}_3, \mathrm{M}\mathrm{g}\underset{\_}{\mathrm{S}{\mathrm{O}}_4}, \mathrm{C}\mathrm{a}\underset{\_}{\mathrm{C}{\mathrm{O}}_3}, \underset{\_}{\mathrm{N}{\mathrm{a}}_2}\mathrm{O}, \underset{\_}{\mathrm{C}\mathrm{a}}\mathrm{O},\underset{\_}{ \mathrm{C}\mathrm{a}}{\left(\mathrm{O}\mathrm{H}\right)}_2,\underset{\_}{ \mathrm{F}\mathrm{e}}\mathrm{S}{\mathrm{O}}_4,$
$\underset{\_}{\mathrm{F}\mathrm{e}}\mathrm{C}{\mathrm{l}}_3,\underset{\_}{ \mathrm{F}{\mathrm{e}}_2}{\mathrm{O}}_3, \mathrm{N}\mathrm{a}\underset{\_}{\mathrm{O}\mathrm{H}}, \underset{\_}{\mathrm{A}\mathrm{l}}{\left(\mathrm{O}\mathrm{H}\right)}_3,\underset{\_}{ \mathrm{N}{\mathrm{a}}_2}\mathrm{C}{\mathrm{o}}_3$

What is balanced chemical equation? Why should a chemical equation be balanced?

Name two elements that have variable valency. Give the formula and name of two compounds formed by each of these elements.

What is a group of atoms of two or more elements behaving like an atom and having a valency is called?

What do you mean by the valency of an element?