What pair of substances would most likely result in the production of a solid when reacting with a base

Both soluble metal salt and carbon dioxide may react with a base to form a solid or what we call a precipitate,

when [oh-] is 10-5  m, and [h3o+] is 10-9  m, the poh is 5 and ph is 9. again in both cases the sum of ph and poh is 14. however, the hydrogen ion concentration is not always going to be equal to exactly 1 x 10 raised to a negative number. for example, we skipped over the value of 2.0 x 10-7.

you need to have a picture of the atom that way we can answer it