We know that combined wave function is given as:

Ψ _{AB} = Ψ_{covalent} + λΨ_{ionic}

The percent ionic character is given by:

[λ^{2}/(1 + λ^{2})] X 100

Therefore, 20 = 100*[λ^{2}/(1 + λ^{2})]

20 + 20 λ^{2} = 100λ^{2}

20 = 100λ^{2} – 20λ^{2}

20 = 80λ^{2}

Therefore, λ^{2} = 20/80

Hence, λ=(20/80) ^{1/2}= 0.5

Thus, the fraction of contribution of ionic character to Ψ _{AB} is 0.5

excellent. . . . . i lyk it. . .

very helpful and brilliantly done