During a reaction of oxalic acid, potassium chlorate and sulphuric acid, the oxidation number of which of the element undergoes a maximum change

The correct option is Cl.

To determine which element undergoes the maximum change in oxidation number during the reaction, let us analyze the oxidation states of the elements in both the reactants and the products of this redox reaction.

The chemical reaction involves oxalic acid ($H_2{C}_2{O}_4$), potassium chlorate ($KCl{O}_3$), and sulphuric acid ($H_{2}S{O}_4$). In this reaction, oxalic acid is oxidized by potassium chlorate in an acidic medium provided by sulphuric acid.

The chemical equation for this redox reaction is:
$3H_2{C}_2{O}_4+KCl{O}_3\to KCl+6C{O}_2+3H_{2}O$
(Note: Sulphuric acid acts as the reaction medium and its sulfate ion does not participate directly in the redox changes).

Let us calculate the changes in the oxidation states of the key elements involved:

1. Chlorine (Cl):
In potassium chlorate ($KCl{O}_3$):
Let the oxidation state of Cl be x.
Potassium (K) has a fixed oxidation state of +1 and Oxygen (O) typically has -2.
$+1+x+3(-2)=0$
$x-5=0\Rightarrow x=+5$
In the product potassium chloride ($KCl$), Chlorine is in the chloride form ($C{l}^{-}$) with an oxidation state of -1.
Therefore, the change in the oxidation number of Chlorine is:
$|+5-(-1\left)\right|=6$

2. Carbon (C):
In oxalic acid ($H_2{C}_2{O}_4$):
Let the oxidation state of C be y.
Hydrogen (H) has an oxidation state of +1 and Oxygen (O) has -2.
$2(+1)+2y+4(-2)=0$
$2+2y-8=0\Rightarrow 2y=6\Rightarrow y=+3$
In the product carbon dioxide ($C{O}_2$):
Let the oxidation state of C be z.
$z+2(-2)=0\Rightarrow z=+4$
Therefore, the change in the oxidation number of Carbon is:
$|+4-3|=1$

3. Sulfur (S):
Sulphuric acid ($H_{2}S{O}_4$) provides the acidic medium, and the sulfate ions ($S{O}_4^{2-}$) do not undergo any redox transformation. The oxidation state of Sulfur remains +6 throughout the reaction. Thus, the change in its oxidation number is 0.

4. Hydrogen (H) and Oxygen (O):
The oxidation states of Hydrogen (+1) and Oxygen (-2) remain constant in both reactants and products, meaning their change in oxidation number is 0.

Comparing all the elements, Chlorine (Cl) undergoes the maximum change in oxidation number, changing by 6 units (from +5 to -1).