When \( \text{Ag}_2\text{S} \) dissolves in \( \text{KCN} \), silver ions (\( \text{Ag}^+ \)) react with cyanide ions (\( \text{CN}^- \)) to form a soluble complex ion. The reaction involves the coordination of two cyanide ions around each silver ion, forming the complex ion \( [\text{Ag(CN)}_2]^- \). This is called the **dicyanoargentate(I)** ion.
The formation of the complex ion can be represented as:
\[ \text{Ag}^+ + 2\text{CN}^- \rightarrow [\text{Ag(CN)}_2]^- \]
The oxidation state of silver in the complex ion is \( +1 \), and the prefix "di-" indicates that two cyanide ligands are coordinated to the silver ion. Thus, the correct name of the complex ion is **dicyanoargentate(I) ion**.
Final Answer: The name of the complex ion is \( \mathbf{\text{dicyanoargentate(I) ion}} \), which corresponds to option \( \mathbf{(2)} \).
A substance 'X' (1.5 g) dissolved in 150 g of a solvent 'Y' (molar mass = 300 g mol$^{-1}$) led to an elevation of the boiling point by 0.5 K. The relative lowering in the vapour pressure of the solvent 'Y' is $____________ \(\times 10^{-2}\). (nearest integer)
[Given : $K_{b}$ of the solvent = 5.0 K kg mol$^{-1}$]
Assume the solution to be dilute and no association or dissociation of X takes place in solution.