When salt loses its water of crystallization to the atmosphere on exposure, the process is said to be

Step 1: Analyze the question The question asks for the term describing a crystalline salt that loses its water of crystallization to the atmosphere when exposed to air.

Step 2: Explain the concepts

• Efflorescence: A hydrated salt loses some or all of its water of crystallization to the air on exposure, often turning into a powder. Example: washing soda, Na₂CO₃·10H₂O, becomes Na₂CO₃·H₂O, a white powder.
• Deliquescence: A substance absorbs so much moisture from the atmosphere that it dissolves in it and forms a solution. Examples: NaOH pellets, CaCl₂, FeCl₃.
• Effervescence: The bubbling or fizzing of a gas escaping from a liquid, such as CO₂ in a soft drink or when acid reacts with a carbonate.
• Fluorescence: The emission of light by a substance after it absorbs radiation. It has nothing to do with water.

Step 3: Apply to the question The salt is losing water of crystallization to the atmosphere. This matches the definition of efflorescence.

• B is wrong because deliquescence involves gaining water.
• C is wrong because effervescence involves gas bubbles.
• D is wrong because fluorescence involves light emission.

Step 4: Answer The correct option is A. efflorescence.

Tip: Remember it with the "E" words: Efflorescence = Exits (water leaves the crystal). Deliquescence = Drinks in water (and Dissolves).