JEE Main 2025 · 2 April · morning · Single correct · +4 / −1

If equal volumes of A B₂ and X Y (both are salts) aqueous solutions are mixed, which of the following combination will give a precipitate of AY₂ at 300 K ? (Given Kₛₚ( at 300 K ) for AY₂=5.2 × 10⁻⁷ )

  1. (a) 2.0 × 10⁻⁴ M AB₂, 0.8 × 10⁻³ M XY
  2. (b) 2.0 × 10⁻² M AB₂, 2.0 × 10⁻² M XY
  3. (c) 1.5 × 10⁻⁴ M AB₂, 1.5 × 10⁻³ M XY
  4. (d) 3.6 × 10⁻³ M AB₂, 5.0 × 10⁻⁴ M XY
Answer and solution

Answer (b) 2.0 × 10⁻² M AB₂, 2.0 × 10⁻² M XY

Solution

Chemistry ma’am · 2 steps

Halve each concentration for the mixing, square [Y⁻], and see which Q beats Kₛₚ.

  1. Ions that matter. AB₂ gives one A²⁺ per formula unit and XY gives one Y⁻. Mixing equal volumes doubles the volume, so each ion's concentration is halved.

    Q = [A²⁺][Y⁻]² precipitate forms only if Q > Kₛₚ = 5.2 × 10⁻⁷

    Option[A²⁺] after mixing (M)[Y⁻] after mixing (M)QPrecipitate?
    (a)1.0 × 10⁻⁴4.0 × 10⁻⁴1.6 × 10⁻¹¹no
    (b)1.0 × 10⁻²1.0 × 10⁻²1.0 × 10⁻⁶yes, Q > Kₛₚ
    (c)7.5 × 10⁻⁵7.5 × 10⁻⁴4.2 × 10⁻¹¹no
    (d)1.8 × 10⁻³2.5 × 10⁻⁴1.1 × 10⁻¹⁰no
  2. So. Only in (b) does the ionic product, 1.0 × 10⁻⁶, exceed 5.2 × 10⁻⁷, so AY₂ precipitates.

The idea to keep. To predict precipitation, compare the ionic product Q with Kₛₚ. Use concentrations after mixing, and raise each ion to its stoichiometric power.

Answer from the NTA final answer key. Solution by PrepWiser.

Study Ionic Equilibrium

Asked about 100 times in JEE Main since 2020. This question is from 2025.