A crystal that absorbs water vapor from the air is

C. hygroscopic

Does it form solution?

If yes, then B.) deliquescent

If no, then C.) hygroscopic

Explanation:

When a substance is exposed to air, it either gives off or absorbs water (moisture) from the air. These phenomenons are explained in Efflorescence, Hygroscopy, and Deliquescence

Hygroscopic and deliquescent materials are both able to absorb moisture from the air. But while hygroscopic materials (e.g NaCl, silica gel) absorb moisture and become damp and sticky, deliquescent materials (e.g. CaCl2 and solid NaOH) dissolves in water absorbed from the air and liquefy.