Question

The organic prefix "but-" means that the organic compound has how many carbon atoms?

Answer 1

You mean `"butyl"`, and this is a `C_4` group.

Explanation:

`"n-Butane"` `=` `H_3C-CH_2CH_2-CH_3`.

`"isobutane"` `=` `H_3C-CH(CH_3)CH_3` or `HC(CH_3)_3`.

Of course, when the `"butyl"` group is substituted somewhere we get a `C_4H_9` residue.