Which of the following is a symptom of gingivitis?

Swollen gums are a primary symptom of gingivitis, which is an inflammation of the gum tissue. In the case of gingivitis, the gums become irritated and swollen due to plaque buildup on the teeth. This condition is often associated with poor oral hygiene, leading to the accumulation of bacteria, which can cause inflammation and redness in the gum tissues. As the inflammation progresses, the gums can become tender and bleed easily during brushing or flossing.

The other symptoms listed, such as painful chewing or loose teeth, are more indicative of more advanced periodontal diseases, like periodontitis, which involve deeper tissue damage and support loss. Black spots on teeth typically suggest dental caries rather than gum disease. Thus, swollen gums are a clear and direct sign of gingivitis, marking it as the correct answer.