Heating phthalic anhydride and concentrated sulfuric acid with which of the following yields phenolphthalein?

$A$ reaction of phenol with chloroform in the presence of sodium hydroxide to form salicylaldehyde is known as

What will be the product,when salicylic acid,obtained by the Reimer-Tiemann process,is reduced with $Zn$ dust?

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 $(10.0)$

Which of the following is the strongest Bronsted acid?

The structure of the product $P$ of the following reaction is