The chemical used in breather for transformer should have the quality of

The correct answer is: B. absorbing moisture.

A breather is a device that is used to prevent the ingress of moisture and dirt into a transformer, while allowing the escape of any gases that may be generated inside. The chemical used in a breather should have the quality of absorbing moisture, so that it can prevent the build-up of moisture inside the transformer, which can lead to corrosion and other problems.

Option A is incorrect because ionizing air is not necessary for a breather to function properly. Option C is incorrect because cleansing the transformer oil is not a function of a breather. Option D is incorrect because cooling the transformer oil is not a function of a breather.