Which element from following is radioactive?

Which element from following is radioactive?
  1. Pr
  2. Nd
  3. Pm
  4. Sm

Solution

Promethium is a chemical element with the symbol $\mathrm{Pm}$ and atomic number 61. All of its isotopes are radioactive; it is extremely rare, with only about 500-600 grams naturally occurring in Earth's crust at any given time.

Asked in: MHT CET 2021 (22 Sep Shift 2)

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