Introduction:
Potassium maleate and potassium fumarate are both organic salts of potassium and have similar chemical structures. However, they differ in terms of their molecular structure and properties. In this response, we will discuss the differences between potassium maleate and potassium fumarate in detail.

1. Molecular Structure:
- Potassium Maleate: Potassium maleate has the chemical formula K2C4H2O4. It is derived from maleic acid, which is a dicarboxylic acid with two carboxyl groups. The maleate ion (C4H2O4^2-) forms the anion in this compound.
- Potassium Fumarate: Potassium fumarate has the chemical formula K2C4H2O4. It is derived from fumaric acid, which is also a dicarboxylic acid but with a different arrangement of carboxyl groups. The fumarate ion (C4H2O4^2-) forms the anion in this compound.

2. Solubility:
- Potassium Maleate: Potassium maleate is sparingly soluble in water. It has a solubility of approximately 2.74 g/100 mL at 20°C.
- Potassium Fumarate: Potassium fumarate is more soluble in water compared to potassium maleate. It has a solubility of approximately 16.1 g/100 mL at 20°C.

3. Stability:
- Potassium Maleate: Potassium maleate is relatively stable under normal conditions. It can withstand moderate heat and does not easily decompose.
- Potassium Fumarate: Potassium fumarate is also stable under normal conditions. It is not easily decomposed by heat.

4. Applications:
- Potassium Maleate: Potassium maleate is primarily used in the pharmaceutical industry as an intermediate for the synthesis of various drugs. It is also used in the production of polymers, adhesives, and coatings.
- Potassium Fumarate: Potassium fumarate is commonly used as a food additive, particularly in the production of beverages and baked goods. It is also used as a dietary supplement due to its role as a source of potassium.

5. Biological Activity:
- Potassium Maleate: Potassium maleate has been studied for its potential biological activities, including antioxidant and anticancer properties. It has shown promising results in certain preclinical studies.
- Potassium Fumarate: Potassium fumarate has also been investigated for its biological activities. It has been found to have antioxidant and anti-inflammatory effects, and it may have potential applications in the treatment of certain diseases.

Conclusion:
In summary, potassium maleate and potassium fumarate are similar in many ways but differ in their molecular structure, solubility, applications, and potential biological activities. While potassium maleate is commonly used in the pharmaceutical industry, potassium fumarate finds applications as a food additive and dietary supplement. Both compounds exhibit stability under normal conditions and have been studied for their biological properties.