When answering a question like that, most of my uncertainty is uncertainty about my interpretation of the question rather than my expectations about the world. I expect my cells to continue functioning and my computer to continue working (p> 80 decibans and 70 decibans respectively), if I mix HCl and NaOH I still expect to get saltwater (p > 60 decibans), and if I shoot a beam of ionized Hydrogen atoms through a magnetic field in a vaccuum, I expect that the beam will curve with a specific radius. If I replace the ionized Hydrogen with ionized Lithium and keep all other factors the same, I expect that radius to approximately seven times that of the beam ofHydrogen atoms (with a few atoms curving at a radius of 6 times that of the Hydrogen if they're some Lithium-6 mixed in) (p > 60 decibans). I expect nuclear fission to continue working, and so expect that some atoms will be divisible into multiple smaller atoms, though that manifests as a belief that nuclear power plants will keep working (p > 60 decibans).
On the other hand, I expect that I understand your question, but not with anywhere near the level of certainty as I have that I will continue to see the physical processes above operating as I've observed them to operate in the past. And even with you saying it's not a trick question, I'm more certain that the predictions made by atomic theory will provide an accurate enough description of reality for my purposes than that this isn't a trick question. And I'm almost positive this isn't a trick question.
That's about as ideal a response as I could ask for; thank you kindly for taking the time to write it out.
How much confidence do you place in the scientific theory that ordinary matter is made of discrete units, or 'atoms', as opposed to being infinitely divisible?
More than 50%? 90%? 99%? 99.9%? 99.99%? 99.999%? More? If so, how much more? (If describing your answer in percentages is cumbersome, then feel free to use the logarithmic scale of decibans, where 10 decibans corresponds to 90% confidence, 20 to 99%, 30 to 99.9%, etc.)
This question freely acknowledges that there are aspects of physics which the atomic theory does not directly cover, such as conditions of extremely high energy. This question is primarily concerned with that portion of physics in which the atomic theory makes testable predictions.
This question also freely acknowledges that its current phrasing and presentation may not be the best possible to elicit answers from the LessWrong community, and will be happy to accept suggestions for improvement.
Edit: By 'atomic theory', this question refers to the century-plus-old theory. A reasonably accurate rewording is: "Do you believe 'H2O' is a meaningful description of water?".