Question

Given,$n - $factor of $KI$ when treated with acidified $KMn{O_4}$ solution is
1. $6$
2. $3$
3. $5$
4. $1$

Answer 1

Hint: n-factor also known as the valence factor or conversion factor. In a redox reaction the n-factor is equal to the number of moles of lost or gained electron per molecule while the n-factor for a substance in a non-redox reaction is equal to the product of displaced mole and its charge. Moreover, the n-factor of a compound is not fixed, it depends on the type and to the extent of the reaction the compound undergoes.

Complete answer:
n-factor for an acid is defined as the number of ${H^ + }$ ions replaced by one mole of acid in a reaction whereas, n-factor for a base is defined as the number of $O{H^ - }$ ions replaced by one mole of a base in a reaction. When KI is treated with acidified $KMn{O_4}$ the reaction proceeds as follows:
$2KMn{O_4} + 10KI + 8{H_2}S{O_4} \to 6{K_2}S{O_4} + 2KMnS{O_4} + 5{I_2}$
In the above reaction Manganese in $KMn{O_4}$ with oxidation number of +7 is reduced to $KMnS{O_4}$ with oxidation number of +2 i.e. it gains five electrons while ${I^ - }$ with oxidation state of -1 is oxidized to ${I_2}$ with oxidation state of zero i.e. loss of one electron thus potassium permanganate acts as an oxidizing agent whereas potassium iodide acts as an reducing agent. Moreover, the n-factor for a redox reaction is equal to the number of lost or gained electrons per molecule. So, as one electron is lost by the reactant, therefore the n- factor when KI is treated with acidified potassium permanganate is one.
Therefore the correct answer is option 1.

Note:
The reaction in which oxidation reaction and reduction reaction takes place simultaneously is called redox reaction. Oxidation reaction involves the either removal of hydrogen or an electropositive element or loss of electron or addition of oxygen or electronegative element while reduction reaction involves either removal of oxygen or an electronegative element or gain of electron or addition of hydrogen or electropositive element.