Question

Why is the total dipole moment of the non-polar molecule is zero?

1.

because the centre of mass of positive charge doesn't coincide with the centre of negative charge

2.

because the centre of positive and negative charges coincides 

3.

because half of the centre of mass of positive charge coincides with half of the centre of mass of negative charge

4.

because half of the centre of mass of negative  charge coincides with half of the centre of mass of positive  charge

Answer 1

Correct Answer - Option 2 :

because the centre of positive and negative charges coincides 

CONCEPT: 

• There two types of molecules, polar and non-polar molecules
  • Polar molecules are molecules in which the centre of positive and negative charge doesn't coincide with one another. 
  • Non-polar molecules are molecules in which the centre of positive and negative charge coincide with one another.
  • Molecules formed upon the bonding of two same elements are homo diatomic molecules

EXPLANATION:

• Non-polar molecules are molecules in which the centre of positive and negative charge coincide with one another.
• Since the centre of positive and negative charges coincides with one another, thus these molecules have zero dipole moment. Hence option 2 is the answer
• Polar molecules are molecules in which the centre of positive and negative charge doesn't coincide with one another. 

• Since the centre of positive and negative charges don't coincide with one another these molecules have non zero diploe moment. 
• The diploe moment of a homo diatomic molecule and symmetric top molecules is zero.