# What is the difference between a strong base and a weak base?

A strong base is a base that ionises or dissociates almost 100% in water to form $O {H}^{-}$ ion. An example of a strong base is sodium hydroxide. It dissociates in water to form sodium ion and hydroxide ion.
A weak base is a base that ionises or dissociates only partially in water to form$O {H}^{-}$ ion. An example of it will be ammonia. It only dissociates partially to form ammonium hydroxide.