Which of the following complex formed by `Cu^(2+)` ions is most stable?

Options

A. `Cu^(2+) + 4NH_(3) hArr [Cu(NH_(3))_(4)]^(2+)`, logK = 11.6
B. `Cu^(2+) + 4CN hArr [Cu(CN)_(4)]^(2-)`, logK = 27.3
C. `Cu^(2+) + 2en hArr [Cu(en)_(2)]^(2+)`, logK = 15.4
D. `Cu^(2+) + 4H_(2)O hArr [Cu(H_(2)O)_(4)]^(2+)`, logK = 8.9

Answer

2

Explanation

The greater the value of log K, the greater will be stability of complex compound formed. For reaction.
`Cu^(2+) + 4CN^(-) to [Cu(CN)_(4)]^(2-)`
`K = ([Cu(CN)_(4)]^(2-))/([Cu^(2+)][Cn^(-)]^(4))` and log K = 27.3
For this reaction, log K has highest value among the given four reactions. Hence, K will also be higher among these four, i.e., stability of the complexes will be highest among these four complexes.