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Unilorin Post-UTME Chemistry 2021 (Model questions) Question 4

Question 4

Atomic Structure

An element with mass number 133 and atomic number 55 has

  1. A.55 electrons and 55 neutron
  2. B.55 electrons and 78 neutron
  3. C.78 electrons and 78 neutron
  4. D.78 electrons and 55 neutron
Show the answer and explanation

Answer: B (55 electrons and 78 neutron)

Explanation

A neutral atom has as many electrons as protons (55); neutrons = 133 − 55 = 78.