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Chemistry Question 52 – NEET-UG 2026

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The correct order of solubility of the given salts in water at 298 K is SaltKsp at 298 KAgBr5.0×10−13Zn(OH)21.0×10−15Hg2Cl21.3×10−18

The solubility product constant (Ksp) is a measure of the solubility of a sparingly soluble ionic compound in a saturated solution.

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Ninja Strategy•Identify Least Soluble First

Identify the salt with the significantly smallest Ksp (Hg2Cl2) as the least soluble, eliminating options that place it higher. Then, compare the remaining two by calculating their solubilities.

Step 1: Determine Stoichiometry and Solubility Expression✦ Active

First, identify the dissociation reaction and the relationship between molar solubility (s) and Ksp for each salt:

AgBr(s)⇌Ag+(aq)+Br−(aq)⟹Ksp=s2⟹s=Ksp Zn(OH)2(s)⇌Zn2+(aq)+2OH−(aq)⟹Ksp=s(2s)2=4s3⟹s=Ksp/43 Hg2Cl2(s)⇌Hg22+(aq)+2Cl−(aq)⟹Ksp=s(2s)2=4s3⟹s=Ksp/43
Step 2: Calculate Molar Solubility for Each Salt○ Expand

Now, substitute the given Ksp values into the respective solubility expressions:

sAgBr=5.0×10−13=50×10−14≈7.07×10−7 M sZn(OH)2=1.0×10−15/43=0.25×10−153=250×10−183≈6.30×10−7 M sHg2Cl2=1.3×10−18/43=0.325×10−183=325×10−213≈6.88×10−8 M
💡 Teacher's Secret Hint

Remember to adjust the exponent for easier cube root calculation (e.g., 10−15 to 10−18 or 10−21).

Step 3: Compare Solubilities and Determine Order○ Expand

Compare the calculated molar solubilities to find the correct order from highest to lowest:

sAgBr(7.07×10−7 M)>sZn(OH)2(6.30×10−7 M)>sHg2Cl2(6.88×10−8 M)

Thus, the correct order of solubility is AgBr>Zn(OH)2>Hg2Cl2.

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