In silver plating of copper \(K[Ag(CN)_2]\)is used instead of \(AgNO_3\). The reason is

less availability of \(Ag^+\) ions as \(Cu\) cannot displace Ag from \([Ag(CN)_2]^-\) ion

The correct answer is option 4. Less availability of Ag⁺ ions as Cu cannot displace Ag from \([Ag(CN)_2]^−\) ion.

In silver plating processes, such as using \(K[Ag(CN)_2]\) instead of \(AgNO_3\), the reason typically revolves around the properties of the silver ions in solution and their ability to deposit onto the substrate (in this case, copper). Let's analyze the given options:

1. A thin layer of Ag is formed on Cu: This is a common objective in silver plating. The goal is to deposit a thin, uniform layer of silver onto the surface of copper.

2. More voltage is required: This statement is not necessarily true. The voltage required for electrodeposition is determined by the reduction potential of the metal ions involved. The specific voltage required can vary depending on the electrolyte and conditions, but it's not directly related to the choice of \(K[Ag(CN)_2]\) versus \(AgNO_3\).

3. \(Ag^+\) ions are completely removed from the solution: This is a possibility in any plating process where metal ions are transferred from the solution to the substrate. However, it's not a specific reason why \(K[Ag(CN)_2]\) might be chosen over \(AgNO_3\).

4. Less availability of \(Ag^+\) ions as \(Cu\) cannot displace \(Ag\) from \([Ag(CN)_2]^−\) ion: This statement correctly explains the reason for choosing \(K[Ag(CN)_2]\) over \(AgNO_3\). In \(K[Ag(CN)_2]\), silver is complexed with cyanide ions \(([Ag(CN)_2]^-)\). These complexes are stable and do not readily release \(Ag^+\) ions into solution. Therefore, when using \K[Ag(CN)_2]\), the silver ions are less available in the solution compared to \(AgNO_3\), where \(Ag^+\) ions are freely available.

The reason why K[Ag(CN)2] is used instead of AgNO3 in silver plating of copper is less availability of \(Ag^+\) ions as \(Cu\) cannot displace Ag from \([Ag(CN)_2]^-\) ion.

This choice ensures that silver ions are not overly concentrated in the solution, which can affect the quality and efficiency of the plating process.