What radioactive element has the lowest atomic number?

The radioactive element with the lowest atomic number among the options you provided is Technetium (Tc), which has the atomic number 43.

Here’s a brief explanation: Atomic numbers are assigned based on the number of protons in an element’s nucleus. While Phosphorus (P, atomic number 15) and Chromium (Cr, atomic number 24) are not radioactive, Technetium is the lightest radioactive element and is primarily used in various applications including medical imaging.

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