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MCQ practice · SSC Physics Board questions · Chapter 13: Radioactivity and Electronics

Rajshahi Board 2021

In uranium-235:

  1. i. there are 92 protons
  2. ii. there are 143 neutrons
  3. iii. the atomic number is 92

Think it through first, then pick an option.

  1. a i and ii
  2. b i and iii
  3. c ii and iii
  4. d i, ii and iii
Answer and explanation

Correct answer: d i, ii and iii

i, ii and iii: protons 92 (the atomic number is 92 too), and neutrons 235 − 92 = 143, so all three are true.

Why the other options are wrong

  • a i and ii: i and ii: both are true, but iii is true too, because the atomic number is the number of protons and the book gives the atomic number of uranium as 92.
  • b i and iii: i and iii: both are true, but ii is true too: the number of neutrons = 235 − 92 = 143.
  • c ii and iii: ii and iii: both are true, but i is true too: an atomic number of 92 means 92 protons in the nucleus.