Which one of the following forms with an excess of `CN^(-)` (Cyanide) a complex having coordination number two

Options

A. `Cu^(+)`
B. `Ag^(+)`
C. `Ni^(2+)`
D. `\Fe^(2+)`

Answer

B

Explanation

The total number of points of attachment to the central element is termed the coordination number and this can vary from 2 to as many as 16,but is usually 6.There is no way to predict the coordination number 2 is not very common for first best known example for silver(1).For instance ,a method often employed for the detection of chloride ions involves the formation of the linear diamminesilver(1)complex the first step is:`Ag^(+)Cl^(-)toAgCl`(white ppt.)
And to ensure that the precipitate is really the chloride salt,two further tests must by done:
`AgCl+2NH_(3)to[Ag(NH_(3))_(2)]^(+)`
and `[(Ag(NH_(3))_(2))]^(+)+HNO_(3)to "AgCl"`(ppts.)The reaction of a bidentate ligand such a1,2-diaminoethane with`Ag^(+)` does not lead to chelated ring systems,but instead to linear two coordinate complexs.One reason for this is that bidenate ligands can not exist in trans arrangments that isd they cannot span 180 degrees.