Hydroxide is a polyatomic ion with the chemical formula OH⁻. It consists of one oxygen atom covalently bonded to one hydrogen atom, and it carries a negative electric charge. In a chemical equation, hydroxide is typically represented as OH⁻. For example:

NaOH (sodium hydroxide) dissociates in water to form Na⁺ and OH⁻ ions:

```

NaOH → Na⁺ + OH⁻

```

Ca(OH)₂ (calcium hydroxide) dissociates in water to form Ca²⁺ and 2OH⁻ ions:

```

Ca(OH)₂ → Ca²⁺ + 2OH⁻

```

Fe(OH)₃ (iron(III) hydroxide) is formed when Fe³⁺ ions react with OH⁻ ions in a precipitation reaction:

```

Fe³⁺ + 3OH⁻ → Fe(OH)₃ (s)

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In organic chemistry, hydroxide is often represented as -OH. For example, ethanol (CH₃CH₂OH) contains a hydroxyl group (-OH) bonded to the carbon atom.