State one use and one harmful effect of radioactivity.

Explanation

**Step-by-Step Solution:**

1. **Identify a Use of Radioactivity:**
- Radioactivity has several applications in various fields. One significant use is in the medical field, specifically in the treatment of cancer. Radioactive isotopes are utilized in radiation therapy to target and destroy cancerous cells.

2. **Identify a Harmful Effect of Radioactivity:**
- While radioactivity has beneficial uses, it also poses risks. One harmful effect of radioactivity is that it can damage living tissues in the human body. This damage can lead to serious health issues, including radiation burns and an increased risk of cancer.

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