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

1 Answer
Dec 27, 2016

Answer:

The correct answer is B oxidized … colourless… brown.

Explanation:

Iodide ions, #"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, #"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"^"-"#