[Karatekboy]

The question is: How do the formula or molecular weights of he following differ: C¹⁶O₂, C¹⁸O₂, and K₂¹⁸O? Explain. Now it is not the problem that is tripping me up as much as the superscript a on the numbers because they are obviously superscripts to the right of the number and they do not have a charge attached to them. An example using this problem would be very helpful!

[AWK]

Superscript on the left of symbol informs you about mass of isotope (in all these cases  - oxygen).

[mikasaur]

http://preparatorychemistry.com/Bishop_Isotope_Notation.htm

[Karatekboy]

Ok, that makes sense. I thought it was attached to the Carbon