What is the difference between\[Cl\], \[C{l_2}\] and\[C{l_3}\]?

Hint: We need to know that the chlorine is an element which belongs to group $17$ i.e. Halogen family in periodic table. Group $17$ has one electron less to attain a noble gas configuration. The elements present in group $17$ are electronegative atoms and have high electron affinity.

Complete answer:
Let’s see the difference between the atoms or molecules given. It is clearly seen from the question that three forms of chlorine are given. \[Cl\] is made up of a single atom of chlorine which is present in elemental form. \[C{l_2}\] is made up of two atoms of chlorine that are combined together by covalent bonds. \[C{l_3}\] is a molecule which is formed by combining three atoms of chlorine. \[C{l_3}\] does not exist in nature. It exists as molecule $AlC{l_3}$, an aluminum atom combined with three chlorine atoms to form an aluminum chloride molecule. \[C{l_2}\] is a molecule consisting of two atoms whereas \[C{l_3}\] is an anion consisting of three atoms. Hence, \[C{l_3}\] has a negative electrical charge, but \[C{l_2}\] is neutral.

Note:
We have to know that chlorine is a yellow-green gas at room temperature. It is an extremely reactive element and a strong oxidizing agent: among the elements, it has the highest electron affinity and the third-highest electronegativity on the Pauling scale, behind only oxygen and fluorine.