Hydrogen catches fire easily and oxygen helps in combusion. Why is water used for extinguishing fire ?

Carbondioxide is used for extinguishing fire because

Carbondioxide is used for extinguishing fire because

Why is CO_(2) used as fire extinguisher ?

Which salt is used in fire extinguishers ?

Give scientific reasons: Hydrogen is combustible, oxygen helps combustion, but water helps to extinguish fire.