Sentence examples for The second reason from inspiring English sources

"The second reason" is correct and usable in written English.
You can use it when you are presenting two or more reasons for something. For example: "There are three reasons why I should get a raise. The first is that I have been working here for five years. The second reason is that I have taken on more projects than anyone else in my department. The third reason is that the quality of my work has always been exceptional."