Verified answer

I would suggest contacting the consumer protection office of your state attorney general's office if you are in the US. There are FTC and so-called mini FTC laws that prohibit false claims or false advertising. You would need to check the statute for any possible relief for individual consumers. Otherwise a stand-alone civil action will get you nowhere unless you can provide evidence of actual damages of a magnitude that would make such a suit worthwhile.

You can sue almost anyone for almost anything. But whether or not you'll win will depend on a lot more specific information. For example, did the lack of this particular ingredient cause you harm? If not, then you won't win any lawsuit. And what do you mean by "company of a company"?

No. You wouldn't have received damages and there's no requirement they put an ingredient in a product....

It would depend on Tort, and a very knowledgeable attorney.