What's the cause behind the replacement of lighter coloured variety of peppered moth(Biston betularia) to its darker variety (Biston carbonaria) in England?

Natural selection.

The correct answer is Option (1)- Natural selection.

The replacement of the lighter-colored variety of the peppered moth (Biston betularia) by its darker variety (Biston carbonaria) in England is caused by natural selection. During the Industrial Revolution in England, many areas became heavily polluted with soot, which darkened the trees and buildings. The lighter-colored moths, which previously had camouflage against lichen-covered trees, became more visible to predators on the soot-darkened surfaces. Conversely, the darker moths were better camouflaged against the soot-darkened trees and thus had a survival advantage. This change in environmental conditions led to natural selection favoring the darker variety of the moth. Over time, the frequency of the darker moths increased, while the lighter moths became less common. This phenomenon is an example of industrial melanism.