August 2018 NY Regents Chemistry Exam
27 What evidence indicates that the nuclei of strontium-90 atoms are unstable?
(1) Strontium-90 electrons are in the excited state.
(2) Strontium-90 electrons are in the ground state.
(3) Strontium-90 atoms spontaneously absorb beta particles.
(4) Strontium-90 atoms spontaneously emit beta particles.
Solution: Table N on the Reference Table gives decay mode for different radioisotopes. Strontium-90 has a beta decay mode.
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