What product is obtained when two moles of acetic acid are heated with $P_2O_5$?

What is the correct order of reactivity of carboxylic acid derivatives towards nucleophilic acyl substitution?

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 $A$ and $B$ in the following reaction:
$CH_3-CH_3 \stackrel{B}{\longleftarrow} CH_3COOH \stackrel{A}{\longrightarrow} CH_3CH_2OH$
$A \quad B$

Acetyl chloride is reduced with $LiAlH_4$. The product formed is:

Identify the major product formed when the following compound is treated with acidic $KMnO_4$.