In the titration of $$KMnO_4$$ and oxalic acid in acidic medium, the change in oxidation number of carbon at the end point is ______.

The balanced chemical equation for the reaction between potassium permanganate and oxalic acid in acidic medium is:

$$\mathrm{2KMnO_4 + 5H_2C_2O_4 + 3H_2SO_4 \rightarrow 2MnSO_4 + K_2SO_4 + 10CO_2 + 8H_2O}$$

Oxalic acid acts as the reducing agent and is oxidised to $$\mathrm{CO_2}$$.

To calculate the change in oxidation number of carbon, determine its oxidation state in both reactant and product.

In oxalic acid $$\mathrm{(H_2C_2O_4)}$$:

Let oxidation state of carbon be $$\mathrm{x}$$.

$$\mathrm{2(+1) + 2x + 4(-2) = 0}$$

$$\mathrm{2 + 2x - 8 = 0}$$

$$\mathrm{2x = 6}$$

$$\mathrm{x = +3}$$

Thus, oxidation state of carbon in oxalic acid is:

$$\mathrm{+3}$$

In carbon dioxide $$\mathrm{(CO_2)}$$:

Let oxidation state of carbon be $$\mathrm{y}$$.

$$\mathrm{y + 2(-2) = 0}$$

$$\mathrm{y - 4 = 0}$$

$$\mathrm{y = +4}$$

Thus, oxidation state of carbon in $$\mathrm{CO_2}$$ is:

$$\mathrm{+4}$$

Therefore, change in oxidation number of carbon:

$$\mathrm{= (+4) - (+3)}$$

$$\mathrm{= 1}$$

$$\boxed{\mathrm{1}}$$