Answer: Sodium Hydroxide (NaOH)
Explanation: Sodium Hydroxide also known as Cautious Soda is a compound comprising of Sodium cations and Hydroxide anions.
It is white and in form of opaque crystals.
It is anhydrous and completely soluble in water.
It is also a Hygroscopic compound which explains its absorption of water from the air.
Sodium Hydroxide is also formed by a chlor alkali process which is an industrial processes used for the electrolysis of sodium chloride solutions.
This process produces sodium hydroxide and chlorine.
See simple equation below;
2NaCl + H2O ---> 2NaOH + Cl2