The gas which is used in detection of metal ions Cu 2 + & Ag + by forming deep blue and colourless compound respectively.

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TestHub · Accepted Answer

The gas used is ammonia (NH₃). With Cu²⁺, it forms the deep blue tetraamminecopper(II) complex, $[C u (N H_{3})_{4}]^{2 +}$ . With Ag⁺, it forms the colourless diamminesilver(I) complex, $[A g (N H_{3})_{2}]^{+}$ , which is used in Tollens' reagent.

Reactions:

$C u^{2 +} (a q) + 4 N H_{3} (a q) \to [C u (N H_{3})_{4}]^{2 +} (a q)$ (deep blue)

$A g^{+} (a q) + 2 N H_{3} (a q) \to [A g (N H_{3})_{2}]^{+} (a q)$ (colourless)

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