What is the formula for peroxide?

The formula for peroxide is represented as O2^2-. This indicates that a peroxide ion consists of two oxygen atoms bonded together, with an overall charge of -2. This bonding arrangement gives peroxides their distinctive properties, such as being strong oxidizing agents.

In the context of the other options, they relate to different compounds with distinct structures and properties. SO4^2- denotes the sulfate ion, which contains sulfur and four oxygen atoms. Cyanide represents a completely different compound featuring carbon and nitrogen. SO3^2- is the sulfite ion, containing sulfur and three oxygen atoms. Each of these ions has its own unique chemical characteristics and does not represent peroxide. Thus, the only option that accurately represents peroxide is O2^2-.