The correct answer is option 2 i.e. Lightening.From the first part of the analogy, it becomes clear that a noun is needed after its corresponding adjective. White is an adjective (color) and it is related to Whitening (noun) that means the act or process of making or becoming white. Similarly, light is also an adjective that means having little weight and it is related to 'lightening' i.e. to reduce in weight or quantity.The meaning of the rest of the options are given below:Lightning: the flashing of light produced by a discharge of atmospheric electricity.Lighting : illumination or ignition.Enlightening: providing or tending to provide knowledge, understanding, or insight.