NCERT Question 17 - Chapter 4 Class 9 - Structure of Atom

Number of valence electrons in Cl – ion are:

(a) 16 (b) 8 (c) 17 (d) 18

Answer

(b) 8

Explanation:

• Valence electrons are the electrons in the last filled shell of an atom.
• Cl has atomic number 17, therefore it has 17 electrons

• Cl ^- has 1 e ^- more than Cl , therefore it will have 18 electrons

• Its electronic configuration is given as follows:
  K Shell = 2 e ^-
  L Shell = 8 e ^-
  M Shell = 8 e ^-

• Since the valence shell(M Shell) has 8 e ^- , the number of valence electrons is 8.