Which type of selection explains industrial melanism observed in moth, Bistonbitularia:

Industrial melanism means evolution of dark-coloured varieties of animals (especially moths) in industrial areas where they are better camouflaged than paler forms.

Stabilising changes in which individual acquire mean characters.

Directional changes in which individual acquire value other than the mean character value.

Disruptive changes in which individual acquire peripheral character value at both ends of the distribution curve.

So industrial melanism is not a character but rather is acquired trait by most of the animals.

So it is an example of directional change.

Hence the correct answer is option (b).