Acetic acid is prepared from methyl magnesium bromide and dry ice in presence of dry ether. Name the compound which serves not only reagent but also as cooling agent in the reaction.

Observe the following equation of the reaction of Tollens’ reagent with an aldehyde. How do we know that a redox reaction has taken place. Explain.

$\mathrm{R}-\mathrm{CHO} + 2\mathrm{Ag}{{\left({\mathrm{NH}}_3\right)}_2}^{+}+{\mathrm{OH}}^{-}\stackrel{∆}{\to }\mathrm{R}-\mathrm{COO}{ }^{-}+ 2\mathrm{Ag} \downarrow + 4{\mathrm{NH}}_3 + 2{\mathrm{H}}_2\mathrm{O}$

Arrange the following carboxylic acids with increasing order of their acidic strength and justify your answer.