Choose the correct tests with respective observations. (A) $\mathrm{CuSO}_{4}$ (acidified with acetic acid) + $\mathrm{K}_{4}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right] \rightarrow$ Chocolate brown precipitate. (B) $\mathrm{FeCl}_{3}+\mathrm{K}_{4}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right] \rightarrow$ Prussian blue precipitate. (C) $\mathrm{ZnCl}_{2}+\mathrm{K}_{4}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]$, neutralised with $\mathrm{NH}_{4} \mathrm{OH}$ → White or bluish white precipitate. (D) $\mathrm{MgCl}_{2}+\mathrm{K}_{4}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right] \rightarrow$ Blue precipitate. (E) $\mathrm{BaCl}_{2}+\mathrm{K}_{4}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]$, neutralised with NaOH → White precipitate. Choose the correct answer from the options given below:

JEE Main · 2025 · 02 Apr 2025 · Shift 1 · Practical and Analytical Chemistry

Choose the correct tests with respective observations.
(A)

CuSO_{4}

(acidified with acetic acid) +

K_{4} [Fe (CN)_{6}] \to

Chocolate brown precipitate.
(B)

FeCl_{3} + K_{4} [Fe (CN)_{6}] \to

Prussian blue precipitate.
(C)

ZnCl_{2} + K_{4} [Fe (CN)_{6}]

, neutralised with

NH_{4} OH

→ White or bluish white precipitate.
(D)

MgCl_{2} + K_{4} [Fe (CN)_{6}] \to

Blue precipitate.
(E)

BaCl_{2} + K_{4} [Fe (CN)_{6}]

, neutralised with NaOH → White precipitate.
Choose the correct answer from the options given below:

(A)A, D and E only
(B)B, D and E only
(C)A, B and C only✓ Correct
(D)C, D and E only

Answer: (C)

Solution

Acidified copper sulphate with potassium ferrocyanide gives the chocolate-brown

Cu X_{2} [Fe (CN) X_{6}]

, ferric chloride gives the deep Prussian-blue

Fe X_{4} [Fe (CN) X_{6}] X_{3}

, and zinc chloride after neutralisation with ammonium hydroxide gives the white to bluish-white

K X_{2} Zn X_{3} [Fe (CN) X_{6}] X_{2}

; all three match their stated observations. Magnesium chloride gives a white ferrocyanide, not a blue solid, so that observation is false, and the barium test as described does not hold either. The correctly paired tests are those of copper, iron(III) and zinc.

JEE Main · 2025 · 02 Apr 2025 · Shift 1 · Single correct option

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JEE Main · 2025 · 02 Apr 2025 · Shift 1 · Practical and Analytical Chemistry

Solution

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