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Chemistry Question 62 – JEE-MAIN 2025

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Choose the correct tests with respective observations. (A) CuSO4 (acidified with acetic acid) + K4[Fe(CN)6] → Chocolate brown precipitate. (B) FeCl3 + K4[Fe(CN)6] → Prussian blue precipitate. (C) ZnCl2 + K4[Fe(CN)6], neutralised with NH4OH → White or bluish white precipitate. (D) MgCl2 + K4[Fe(CN)6] → Blue precipitate. (E) BaCl2 + K4[Fe(CN)6], neutralised with NaOH → White precipitate. Choose the correct answer from the options given below :

Recall the characteristic reactions of various metal ions with potassium ferrocyanide, K4[Fe(CN)6].

● Video Walkthrough
Step 1: Analyze Reactions (A), (B), and (C)✦ Active

Statement (A): Cu2+ reacts with [Fe(CN)6]4− to form Cu2[Fe(CN)6], which is a chocolate brown precipitate. This statement is correct.

Statement (B): Fe3+ reacts with [Fe(CN)6]4− to form Fe4[Fe(CN)6]3, known as Prussian blue. This statement is correct.

Statement (C): Zn2+ reacts with [Fe(CN)6]4− to form Zn2[Fe(CN)6], a white precipitate. Neutralization with NH4OH ensures its formation. This statement is correct.

Step 2: Analyze Reactions (D) and (E)○ Expand

Statement (D): Mg2+ ions do not form a precipitate with K4[Fe(CN)6] under normal conditions; magnesium ferrocyanide is soluble. Thus, this statement is incorrect.

Statement (E): Ba2+ ions do not form a precipitate with K4[Fe(CN)6]; barium ferrocyanide is soluble. Thus, this statement is incorrect.

Step 3: Conclusion○ Expand

Based on the analysis, statements (A), (B), and (C) are correct. Therefore, the option 'A, B and C only' is the correct answer.

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