Which one is a strong base - ammonia or sodium hydroxide?

Sodium Hydroxide is stronger base than Ammonia. Sodium hydroxide (NaOH) dissolved in water, is a strong base. Strong bases are strong electrolytes. For most purposes, strong bases ionize completely in water and produce a significant number of hydroxide ions. read more

A strong base is something like sodium hydroxide or potassium hydroxide which is fully ionic. You can think of the compound as being 100% split up into metal ions and hydroxide ions in solution. Each mole of sodium hydroxide dissolves to give a mole of hydroxide ions in solution. read more