Final answer:
The error in the claim that a supplement is 'completely natural and chemical-free' is that it incorrectly suggests natural substances do not contain chemicals. In fact, everything is composed of chemicals, including all natural substances. Therefore, the correct answer is c) 'Both a and b'.
Step-by-step explanation:
The claim that a dietary supplement is completely natural and chemical-free carries an error because it misrepresents what chemicals are. Both statements a) 'Everything is made up of chemicals' and b) 'Natural substances are also chemicals' are correct, which would make option c) 'Both a and b' the right choice.
By definition, all matter, including natural substances and synthetic ones, is composed of chemicals, which are simply substances with a distinct molecular composition that are produced by or used in a chemical process. Hence, even something labeled 'natural' like fruits, vegetables, and water consist of chemicals. The concern for health and wellness in terms of chemicals typically revolves around avoiding synthetic or man-made chemicals such as preservatives and additives, not chemicals that naturally occur in our food.