Some compounds and their $pK_a$ values are given. Arrange them in decreasing order of their acidic strength.
$(i)$ Ethanol $(15.9)$,Phenol $(10.0)$,Cresol $(10.1)$,Water $(15.7)$
$(ii)$ $o$-Nitrophenol $(7.2)$,$m$-Nitrophenol $(8.3)$,Ethanol $(15.9)$,Water $(15.7)$,Phenol $(10.0)$

(A) The acidic strength is inversely proportional to the $pK_a$ value. Lower $pK_a$ indicates higher acidic strength.
$(i)$ The $pK_a$ values are: Phenol $(10.0) <$ Cresol $(10.1) <$ Water $(15.7) <$ Ethanol $(15.9)$.
Therefore,the decreasing order of acidic strength is: $\text{Phenol} > \text{Cresol} > \text{Water} > \text{Ethanol}$.
$(ii)$ The $pK_a$ values are: $o$-Nitrophenol $(7.2) < m$-Nitrophenol $(8.3) <$ Phenol $(10.0) <$ Water $(15.7) <$ Ethanol $(15.9)$.
Therefore,the decreasing order of acidic strength is: $o\text{-Nitrophenol} > m\text{-Nitrophenol} > \text{Phenol} > \text{Water} > \text{Ethanol}$.