Question

Water is a _______ ?

Answer 1

Hint: Water is always used to dilute acids and bases. If water could itself react with an acid or a base (neutralization reaction) then it would not have been a suitable diluting agent. Moreover solutions of acids and bases can be prepared in water indicating its inertness towards an acid-base reaction.

Complete answer:
Any molecule can be classified as an acid or a base depending upon its reactions with other acids or bases.
According to the Arrhenius Acid-base theory, any chemical compound that releases hydrogen ions (or protons) in aqueous solutions is called an acid and the one that releases hydroxide ions in aqueous solution is called a base.
The strength of an Arrhenius acid is determined by the amount of hydrogen ions \[{H^ + }\] released and that of an Arrhenius base is determined by the amount of hydroxide ions \[O{H^ - }\] released by it. The higher the amount of \[{H^ + }\] ions released, lower will the pH and stronger will be the acid. The higher the amount of \[O{H^ - }\] ions released, higher will be the pH and stronger will be the base.
But water is a neutral molecule on the pH scale. In fact, different acids and bases are compared on the pH scale relative to water which has a pH of 7.
Water on dissociations gives both \[{H^ + }\] as well as \[O{H^ - }\] ions.
\[{H_2}O \rightleftharpoons {H^ + } + O{H^ - }\]
Thus water is a neutral compound according to Arrhenius theory.
But according to the Bronsted-Lowry acid base theory, water can accept as well as donate \[{H^ + }\] ions. It behaves like an acid in presence of a stronger base (gets deprotonated) and a base in the presence of a stronger acid (gets protonated).
Thus water is a neutral molecule according to Arrhenius theory and an amphoteric compound according to the Bronsted-Lowry acid base theory.

Note:
Being neutral is not the same as being amphoteric. Water is neutral because it releases both \[{H^ + }\] as well as \[O{H^ - }\] ions in equal amounts but it is amphoteric according to the Bronsted-Lowry acid base theory as it reacts with both acids and bases.