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Compare with adsorption and sorption . 1. Penetration of molecules into the bulk of a solid or liquid, forming either a solution or compound. Absorption can be a chemical process (a strong solution of NaOH absorbs CO 2 from the air) or a physical process (palladium absorbs hydrogen gas). 2. Capture and transformation of energy by a substance; for example, copper looks reddish because it absorbs blue light. An absorbent captures another material and distributes it throughout; an adsorbent captures another material and distributes it on its surface only.