# Refer to the question below.......please give solid explanation for the answer......?

## Aqueous potassium iodide, KI(aq), can be used as a test reagent in redox reactions. Iodide ions are readily ......X...... . A positive result for the test is when the solution changes colour from ......Y...... to ......Z...... . Which words correctly complete gaps X, Y and Z? $$ X. Y. Z.  A oxidised ...... brown............... colourless B oxidised ....... colourless....... brown C reduced ....... brown.............. colourless D reduced ....... colourless........ brown

Dec 27, 2016

The correct answer is B oxidized … colourless… brown.

#### Explanation:

Iodide ions, $\text{I"^"-}$, have an oxidation number of -1.

They cannot be reduced to a lower oxidation state.

Hence, the iodide ions must be oxidised.

The most likely oxidation product is iodine, ${\text{I}}_{2}$, which has an oxidation number of 0.

An aqueous solution of iodine has a yellow-brown colour.

The equation for the oxidation half-reaction is:

2underbrace("I"^"-""(aq)")_color(red)("colourless") → underbrace("I"_2"(aq)")_color(red)("brown") + "2e"^"-"