Why is cl2 a subcript​

In Cl, the 2 is a subscript because it indicates there are 2 of the same elements. The Lewis structure would display it as Cl-Cl.

On the other hand, a superscript would indicate a specific charge.

All subscripts show the amount of the specific element there is.

An example would be O or N, they both show that there are 2 of the same elements.

If the subscript is outside a parenthesis such as it indicates there are 2 molecules.