Question 14 — Aman was discussing the structure - Questions at the end of the chapter - Chapter 8 - Journey Inside the Atom (Exploration)

Last updated at July 3, 2026 by

Question 14
Aman was discussing the structure of atom with his classmates. During the discussion, he learnt that an element X has a mass number of 35 and contains 18 neutrons. Based on this information, answer the following questions: (i) How many electrons and protons does element X have? (ii) What is its atomic number? (iii) Identify the element X. (iv) Write its electronic configuration. (v) How many valence electrons does it have? (vi) What will be the mass number if two neutrons are added to its nucleus? (vii) What will be the relation of X with the new atom?
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  • (i) Protons = A − neutrons = 35 − 18 = 17; electrons = 17 .
  • (ii) Atomic number = 17 .
  • (iii) Element X = Chlorine (Cl) .
  • (iv) Electronic configuration = 2, 8, 7 .
  • (v) Valence electrons = 7 .
  • (vi) New mass number (2 neutrons added) = 35 + 2 = 37 .
  • (vii) X and the new atom have the same Z but different A → they are isotopes .
Element X (A 35, n 18) Protons equal 35 minus 18 equals 17 So it is chlorine (Z 17) Config 2, 8, 7 means 7 valence electrons
Back to: 8.9.1 Isotopes
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