Beta decay producing barium-137 comes from which parent nucleus? Barium has atomic number 56.

1. Beta-minus decay increases the atomic number of the parent nucleus by one, while the mass number stays the same. 2. Since barium-137 has atomic number 56 as the product, the parent must have atomic number 55. 3. The element with atomic number 55 is cesium, giving cesium-137 as the parent. 4. Xenon (54), lanthanum (57), and iodine (53) do not have atomic number 55. 5. So cesium-137 is correct. _Source: OpenStax Physics (CC BY 4.0), Ch 22 "The Atom", section 22.2 Nuclear Forces and Radioactivity_