Question

What is a pure substance that cannot be broken down by chemical or physical means?

Answer 1

`"An element........."`

Explanation:

There are about 100 or so elements, which are species with identical atomic numbers, `Z`, and which cannot be broken down by chemical means. Of course, some elements may be broken down by physical (i.e. nuclear) means, which explains the phenomena of fission, and radioactivity.