Deliquescent substances are also?

Step 1: Analyze the question The question asks which property a deliquescent substance also has.

Step 2: Explain the concepts

• Deliquescent: a substance that absorbs so much moisture from the air that it dissolves in it and forms a solution. Examples are NaOH, CaCl₂ (anhydrous), and FeCl₃.
• Hygroscopic: a substance that absorbs moisture from the air, without necessarily dissolving. Examples are concentrated H₂SO₄ and CaO. Every deliquescent substance is hygroscopic, but not every hygroscopic substance is deliquescent.
• Efflorescent: the opposite of deliquescent. The substance loses water of crystallisation to the air and turns into powder. Examples are Na₂CO₃·10H₂O and Na₂SO₄·10H₂O.
• Anhydrous: a substance with no water of crystallisation. This describes its composition, not how it behaves in air.
• Insoluble: does not dissolve in water. A deliquescent substance dissolves in the water it absorbs, so it is certainly not insoluble.

Step 3: Go through the options

• A. Efflorescent: it loses water, so it is the opposite. ✗
• B. Anhydrous: not a property that follows from deliquescence. ✗
• C. Hygroscopic: deliquescent substances absorb water from the air, so they are hygroscopic. ✓
• D. Insoluble: contradicts deliquescence. ✗

Answer: C. hygroscopic

Exam tip: Remember it this way:

• Deliquescent = absorbs water and dissolves (becomes liquid, since "liquesce" means to become liquid).
• Hygroscopic = absorbs water (the umbrella term).
• Efflorescent = loses water (think "flour": it turns powdery).