which of the following is a redox reaction ?

Options

A. `NaCl + KNO_(3) to NaNO_(3) + KCl`
B. `CaC_(2)O_(4) + 2HCl to CaCl_(2) + H_(2)C_(2)O_(4)`
C. `Ca(OH)_(2) + 2NH_(4)Cl to CaCl_(2) + 2NH_(3) + 2H_(2)O`
D. `2K[Ag(CN)_(2)] + Zn to 2Ag + K_(2)[Zn(CN)_(4)]`

Answer

D

Explanation

(a) `overset(+1)Naoverset(-1)(Cl) + overset(+5)K overset(-2)(NO_(3)) to overset(+1)(Na)overset(+5)Noverset(-2)(O_(3)) + overset(+1)Koverset(-1)(Cl)`
(b) `overset(+2)(Ca)overset(+3)(C_(2))overset(-2)(O_(4)) + 2overset(+1)Hoverset(-1)(Cl) to overset(+2)(Ca)overset(-1)(Cl_(2)) + 2overset(+2)(Ca)overset(-1)(Cl_(2)) + 2overset(-3)overset(+1)H_(3) + 2overset(+1)(H_(2))overset(-2)O`
(c) `overset(+2)(Ca)overset(-1)(OH)_(2) + 3overset(-3)(NH_(4))overset(-1)(Cl) to overset(+2)(Ca)overset(-1)(Cl_(2)) + 2overset(-3)Noverset(+1)(H_(3)) + 2overset(+1)H_(2)overset(-2)O`
In all these cases, during reaction there is no change in oxidation state of ion or molecule or constituent atom, there are simple ionic reactions.
(d) `2K[Ag(CN)_(2)] + Zn to 2Ag + K_(2)[Zn(CN)_(4)]`
`Ag^(+) to Ag`, gain of electron, reduction
`Zn to Zn^(2+)`, loss of electron, oxidation