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Unilorin Post-UTME Chemistry 2021 (Model questions) Question 3

Question 3

Radioactivity

An atom X decays by alpha particle emission to give an atom Y. The atomic number and mass number of Y are

  1. A.90 and 234 respectively
  2. B.91 and 238 respectively
  3. C.92 and 236 respectively
  4. D.93 and 238 respectively
Show the answer and explanation

Answer: A (90 and 234 respectively)

Explanation

Alpha emission removes 2 protons and 4 nucleons. Taking X as uranium-238 (Z = 92), Y has Z = 90 and A = 234; only option A shows a fall of 2 and 4.