Question

Hydrogen being a highly inflammable gas and oxygen being a supporter of combustion, yet water which is a compound made up of hydrogen and oxygen is used to extinguish fire. Why?

Answer 1

Hint :Elements are substances which contain only one type of atom in their structure. They are pure and are arranged in periodic tables to make their study easier. Compounds are formed when a fixed ratio of two or more than two elements are combined chemically to form bonds which keep them together.

Complete Step By Step Answer:
Hydrogen which is an element has its own properties due to the atoms it has like hydrogen is highly inflammable. This is the property of hydrogen atoms. Oxygen is also an element which has its own properties, which are governed by its atoms. As oxygen atoms have the property to support combustion reactions.

Whereas, a water is a compound, and compounds have properties different from its constituents and the constituents cannot retain their own properties when combined. Thus water which is made up of hydrogen and oxygen in a fixed ratio of $ 1:8 $ by mass, has properties which are very different from its elements. Water is used as a fire extinguisher whereas both of its elements have very contrast properties.
 $ 2{H_2} + {O_2} \to 2{H_2}O $
Water is generally present as liquid in state at room temperature whereas hydrogen and oxygen both are gases. Thus physical properties of compounds also differ from the elements.

Note :
Water present in rivers or oceans the structure of water remains always the same and the ratio with which the elements combine to form the compounds also does not change.