Compound $$\left( A \right),\,{C_8}{H_9}Br,\,\,\,$$ gives a white precipitate when warmed with alcoholic $$AgN{O_3}.$$ Oxidation of $$(A)$$ gives an acid $$\left( B \right),$$ $${C_8}{H_6}{O_4}.\,\,\left( B \right)$$ easily forms anhydride on heating. Identify the compound $$(A).$$

Arrange the following compounds in order of decreasing acidity :

An organic compound A upon reacting with $$N{H_3}$$ gives $$B.$$ On heating $$B$$ gives $$C.$$ $$C$$ in presence of $$KOH$$ reacts with $$B{r_2}$$ to given $$C{H_3}C{H_2}N{H_2}2.$$ $$A$$ is :

The expression $${{\tan {\rm A}} \over {1 - \cot {\rm A}}} + {{\cot {\rm A}} \over {1 - \tan {\rm A}}}$$ can be written as: