Everything has a name, but it is generally a “systematic” name[1] rather than a one-off descriptive name. Even DNA is a systematic name for the monomer (de-oxy-ribose-nucleic-acid is one of the defined nucleic acids bound to a ribose sugar missing an oxygen at the 2-position carbon).

Biology uses an enormous space of small molecule structures (to say nothing of proteins, which have their own naming schemes) and few have names you might recognize generally, but all have useful systematic names that biologists and chemists can quickly parse.

As a twist, most systematic naming schemes don’t produce unique labels, so there’s often multiple ways to say the same thing, and different discipline subcultures have different biases in this regard.

Edit: re-reading OP, another interpretation is that they’re asking what percent of molecules in the body aren’t involved in biology. The answer to that is probably something that approximates 0%. At the end of the day, the combined interaction of all of this chemistry is what biology is, and everything is more or less everywhere. (…concentration is everything.)

[1] https://en.m.wikipedia.org/wiki/Systematic_name#In_chemistry