An isotope of iodine is used for making tincture iodine, which is used as a medicine.

Explanation

**Step-by-Step Solution:**

1. **Understanding Isotopes**:
- Isotopes are variants of a chemical element that have the same number of protons but different numbers of neutrons. This means they have the same atomic number but different atomic masses.

2. **Identifying Iodine Isotopes**:
- Iodine has several isotopes, with I-127 being the most stable and common isotope used in various applications, including medicine.

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