Where are you most likely to find the main idea of a news article? in the byline in the first paragraph in the headline in the conclusion

The correct option is in the headline.

In a news article, a reader will most likely find the central idea in the headline. The main function of the headline is to grab people's attention so they continue reading the whole article. As a consequence, the main idea should be in some way expressed here so that the reader knows what the author wants to communicate.