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JEE Advanced · Chemistry · 23. Coordination Compounds

Paragraph:
When a metal rod \(M\) is dipped into an aqueous colourless concentrated solution of compound \(\mathrm{N}\), the solution turns light blue. Addition of aqueous \(\mathrm{NaCl}\) to the blue solution gives a white precipitate \(\mathrm{O}\). Addition of aqueous \(\mathrm{NH}_3\) dissolves \(\mathrm{O}\) and gives an intense blue solution.
Question:
The final solution contains

  1. A \(\left[\mathrm{Pb}\left(\mathrm{NH}_3\right)_4\right]^{2+}\) and \(\left[\mathrm{CoCl}_4\right]^{2-}\)
  2. B \(\left[\mathrm{Al}\left(\mathrm{NH}_3\right)_4\right]^{3+}\) and \(\left[\mathrm{Cu}\left(\mathrm{NH}_3\right)_4\right]^{2+}\)
  3. C \(\left[\mathrm{Ag}\left(\mathrm{NH}_3\right)_2\right]^{+}\)and \(\left[\mathrm{Co}\left(\mathrm{NH}_3\right)_4\right]^{2+}\)
  4. D \(\left[\mathrm{Ag}\left(\mathrm{NH}_3\right)_2\right]^{+}\)and \(\left[\mathrm{Ni}\left(\mathrm{NH}_3\right)_6\right]^{2+}\)
Verified Solution

Answer & Solution

Correct Answer

(C) \(\left[\mathrm{Ag}\left(\mathrm{NH}_3\right)_2\right]^{+}\)and \(\left[\mathrm{Co}\left(\mathrm{NH}_3\right)_4\right]^{2+}\)

Step-by-step Solution

Detailed explanation

Since in the beginning, concentrated \(\mathrm{AgNO}_3\) solution was taken, some \(\mathrm{AgNO}_3\) remain in solution which gives white precipitate of \(\mathrm{AgCl}\) on addition of \(\mathrm{NaCl}\). The precipitate finally dissolve in ammonia and \(\mathrm{Cu}^{2+}\) present in solution also forms complex with ammonia as
\(Cu \left( NO _3\right)_2+4 NH _3( aq ) \rightarrow \underset{\text { Blue }}{\left[ Cu \left( NH _3\right)_4\right]^{2+}}\) \(+~2 NO _3\)
\(AgCl (s)+2 NH _3(a q) \rightarrow\left[ Ag \left( NH _3\right)_2\right]^{+}+ Cl ^{-}\)
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