Question

lemon juice is added gradually to potassium permanganate solution

WRITE CHEMICAL EQUATION AND ONE CHARACTERSTIC

Answer 1

potassium permanganate: KMnO4
lemon juice (citric acid): C6H8O7

reaction:
3KMnO4 + C6H8O7 ---> 3HMnO4 +C6H5K3O7

feature: distinct colour change

Answer 2

Lemon juice is added gradually to potassium permanganate solution is  

$\bold{3 \mathrm{KMnO}_{4}+\mathrm{C}_{6} \mathrm{H}_{8} \mathrm{O}_{7} \rightarrow 3 \mathrm{HMnO}_{4}+\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{K}_{3} \mathrm{O}_{7}}$

Oxidation number of $\mathrm{C}_{6} \mathrm{H}_{8} \mathrm{O}_{7}=+1$

The oxidation number of C in $\mathrm{C}_{6} \mathrm{H}_{3} \mathrm{K}_{3} \mathrm{O}_{7}=1.4$

i.e., Here the oxidation number is increased and H atom (electo +ve) is also removed. In this reaction, citric acid is oxidized.  

Thus, citric acid acts as a reduction agent in this reaction.

By adding the lemon juice to the potassium permanganate, the permanganic acid can be formed which is an inorganic compound. In this reaction, the potassium permanganate will oxidize the lemon juice with the evolving of oxygen or carbon dioxide gas or with a brown precipitate.