(a) $P_{2}O_{5}$ is dehydrating agent, hence acid gives anhydrides on dehydration by $P_{2}O_{5}$. $2RCOOH\underset{- H_{2}O}{\overset{{\ \ \ \ \ P}_{2}O_{5\ }\ \ \ \ \ \ }{\rightarrow}}(RCO)_{2}O$
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