Among the following acids,the strongest acid is

Which acid has the least $pK_a$ value?

Identify the product $(A)$ in the following reaction:
$Ph-CO-Cl + \text{Morpholine} \rightarrow (A) \text{ (Major)}$

Give the reactions of benzoic acid $(C_6H_5COOH)$ with the following:
$(i)$ Sodium metal
$(ii)$ Solution of sodium hydroxide $(NaOH)$
$(iii)$ Solution of sodium bicarbonate $(NaHCO_3)$
$(iv)$ $P_2O_5$ or conc. $H_2SO_4$ $+$ heat
$(v)$ $PCl_5$
$(vi)$ $PCl_3$
$(vii)$ $SOCl_2$
$(viii)$ $NH_3$ $+$ high temperature
$(ix)$ $LiAlH_4$ / ether or $B_2H_6$
$(x)$ Sodalime $(NaOH + CaO)$ $+$ heat
$(xi)$ Conc. $HNO_3$ $+$ conc. $H_2SO_4$ $+$ heat
$(xii)$ $Br_2 + FeBr_3$
$(xiii)$ Oleum $(H_2SO_4 + SO_3)$ $+$ heat

Identify the compound $(B)$ in the following reaction sequence:
$2\text{-formylmethylbenzoic acid}$ $\xrightarrow{NaBH_4} (A)$ $\xrightarrow{H^{\oplus}, \Delta} (B) \text{ (Cyclic)}$

The reaction of an ester $RCOOR'$ with an alcohol $R''OH$ in the presence of an acid gives