An organic substance with the chemical formula C4H2O3 is maleic anhydride. It appears as a crystalline solid that is colourless and pungent-smelling. This substance is a versatile chemical with numerous industrial uses. It is primarily used to make unsaturated polyester resins, which are crucial for producing fibreglass and other composite materials. Pharmaceuticals, agricultural compounds, and alkyd resins can all be made using maleic anhydride. It is useful in organic synthesis due to its reactivity as a dienophile in Diels-Alder processes. Maleic anhydride must be handled carefully and used in accordance with safety precautions because it is extremely irritating to the eyes, skin, and respiratory system.