What is the correct use of an em-dash in a sentence?

An em-dash is often used to indicate a change in thought or introduce a related but distinct idea within a sentence. It creates a strong break that can draw attention to the information that follows, adding emphasis or a dramatic pause that enhances the overall meaning. This versatility makes the em-dash effective in presenting unexpected or contrasting ideas.

For instance, in a sentence like "He was the best player on the team—everyone knew it," the em-dash highlights that the following statement is a significant addition to the first thought, effectively signaling a shift in focus. This use contrasts with other functions of punctuation that might not convey the same level of emphasis or surprise.

The other options explore different uses of punctuation, but they don't fully align with the primary purpose of the em-dash. While an em-dash can indicate a pause, connect thoughts, or separate clauses, its most distinctive and impactful use is to signal a shift or change in thought, making it particularly effective in drawing attention to the additional information that follows.