In neutral solution, potassium permanganate (KMnO4) forms manganese dioxide (MnO2).

Explanation:
Potassium permanganate is a powerful oxidizing agent and undergoes reduction reactions in neutral solutions. It can react with various substances, but in a neutral solution, it tends to react with itself.

The reaction can be represented as follows:
2 KMnO4 + H2O → 2 MnO2 + 2 KOH + 3 [O]

1. Potassium permanganate (KMnO4):
- Potassium permanganate is a purple crystalline solid that is soluble in water. It is highly oxidizing and can react with reducing agents.

2. Neutral solution:
- A neutral solution has a pH of 7, indicating an equal concentration of hydrogen ions (H+) and hydroxide ions (OH-). In a neutral solution, there are no excess hydrogen or hydroxide ions.

3. Formation of manganese dioxide (MnO2):
- In a neutral solution, potassium permanganate undergoes disproportionation, where it is both oxidized and reduced at the same time. This results in the formation of manganese dioxide (MnO2).

The reaction can be divided into two half-reactions:
a) Reduction half-reaction:
- In the reduction half-reaction, two manganese atoms in KMnO4 gain electrons and are reduced to form manganese dioxide (MnO2).
- MnO4- + 4H+ + 3e- → MnO2 + 2H2O

b) Oxidation half-reaction:
- In the oxidation half-reaction, one manganese atom in KMnO4 loses electrons and is oxidized to form manganate ions (MnO4-).
- MnO4- + e- → MnO4^2-

Overall reaction:
- When the reduction and oxidation half-reactions are combined, the net reaction is:
2 KMnO4 + H2O → 2 MnO2 + 2 KOH + 3 [O]

In this reaction, potassium permanganate is reduced to form manganese dioxide, which is a brown solid. The formation of manganese dioxide is indicative of the reduction of permanganate ions to manganous ions (Mn2+).

Therefore, the correct answer is option 'A' - Manganese dioxide.