RMgX + CO 2 → ether dry Y ⟶ H 3 O + RCOOH What is Y in the above reaction?

Grignard reagent on reaction with carbondioxide in presence of dry ether forms an addition product which on hydrolysis produces carboxylic acid.

 Hence,  $\mathrm{Y}$ in the above reaction is ${\mathrm{RCOO}}^{-}{\mathrm{Mg}}^{+}\mathrm{X}$