Answer :
The second example because the colon means after the word warning it is telling you what it is.
Answer:
The answer that shows the proper way to use a colon is Warning: If taken internally, consult a physician immediately.
Explanation:
A colon basically introduces a word, phrase, sentence or list. Whatever is introduced by the colon is emphasized. In this case, as the sentence introduced is a warning, the colon is very useful to highlight that the following message is important.