OH - Hydroxide
Sodium Hydroxide is the compound formed from sodium metal and hydroxide ions. The classic alkali it is more dangerous than most acids since it turns the fats in skin to soap.
Its major uses, in fact, are soap making and unblocking drains. For the latter, the NaOH comes as small white spheres. These are dissolved in hot water to form a solution that is poured down the drain to dissolve away solid matter.