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Question:

In the following reaction sequence in aqueous solution, the species X, Y and Z, respectively, are:
S₂O₃²⁻ + Ag⁺ → X (clear solution) → Y (white precipitate with time) → Z (black precipitate)

[Ag(S₂O₃)₃]⁵⁻, Ag₃SO₃, Ag₂S

[Ag(SO₃)z]³⁻, Ag₂S₂O₃, Ag

[Ag(SO₃)₃]³⁻, Ag₂SO₄, Ag

[Ag(S₂O₃)₂]³⁻, Ag₂S₂O₃, Ag₂S

Solution:

Ag⁺ + 2S₂O₃²⁻ → [Ag(S₂O₃)₂]³⁻ (X)
Ag⁺ + [Ag(S₂O₃)₂]³⁻ → Ag₂S₂O₃ (↓) white ppt. (Y)
(with time) → Ag₂S (↓) Black (Z)