Assuming that the ionic character in H―Br bond is 20 percent. Calculate the fraction of the contribution of the ionic character to the valence bond wave function.

We know that combined wave function is given as:

Ψ _AB = Ψ_covalent + λΨ_ionic

The percent ionic character is given by:
[λ²/(1 + λ²)] X 100

Therefore, 20 = 100*[λ²/(1 + λ²)]

20 + 20 λ² = 100λ²
20 = 100λ² – 20λ²
20 = 80λ²

Therefore, λ² = 20/80

Hence, λ=(20/80) ^1/2= 0.5

Thus, the fraction of contribution of ionic character to Ψ _AB is 0.5