You didn’t add the paragraph, but here’s tips on how to spot the tone:
•Word Choice. Word choice is important when inspecting/deciding the tone of the story. If the tone is serious, you wouldn’t see slang/incorrect terms.
•theme. Theme can sometimes help understand the tone of the story. Sometimes, for an example, if the theme is about family, the tone would most likely be light-hearted or similar.
•The author. Sometimes, authors stick to one tone throughout their books. But, be careful, because sometimes it isn’t the case.