Q14 / 69 · JEE Advanced 2011 (Paper 1) · Chemistry

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 metal $\operatorname{rod} M$ is

  • A
    $\mathrm{Fe}$
  • Correct answer
    B
    $\mathrm{Cu}$
  • C
    $\mathrm{Ni}$
  • D
    $\mathrm{Co}$

Solution

Appearance of blue colour on addition of the metal rod $M$ to the solution of $N$ is an indication that metal may be $\mathrm{Cu}$. Later formation of white precipitate on addition of $\mathrm{NaCl}$ and dissolution of this precipitate in aqueous ammonia confirm that while preipitate is of $\mathrm{AgCl}$. This implies that the solution $N$ is of $\mathrm{AgNO}_3$. This confirm that the metal $M$ is only $\mathrm{Cu}$.

Hence, the correct answer is option: 'B'.

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