Q.Water is a

Water is amphoteric and undergoes a small degree of self-ionisation, or auto-protolysis: $2H_2O \rightleftharpoons H_3O^+ + OH^-$; this equilibrium is significant because it explains water's ability to act as either an acid (donating $H^+$, as when it reacts with the base $NH_3$: $NH_3 + H_2O \rightleftharpoons NH_4^+ + OH^-$) or a base (accepting $H^+$ from a stronger acid like $HCl$), and it underlies the entire pH scale and the definition of neutrality. Water participates in several distinct classes of reaction: hydrolysis, in which a bond of another compound is broken with incorporation of water or its ions, e.g. $Ca_3N_2(s) + 6H_2O(l) \rightarrow 3Ca(OH)_2(aq) + 2NH_3(g)$ and $AlCl_3(g) + 3H_2O(l) \rightarrow Al(OH)_3(s) + 3HCl(aq)$; hydration, a simple addition of water molecules without breaking a bond, e.g. $CaO(s) + H_2O(g) \rightarrow Ca(OH)_2(s)$; and redox reactions, in which water or its component atoms change oxidation state, e.g. its reaction with fluorine, …