An aryl carboxylic acid on treatment with sodium hydrogen carbonate liberates a gaseous molecule. Identify the gas molecule liberated.

The major product formed in the following reaction is
$C_6H_5CH=CH_2$ $\xrightarrow[(ii) H_3O^+]{(i) KMnO_4, KOH, \Delta}$ $\xrightarrow{(iii) Br_2/FeBr_3} \text{Product}$

Grignard reagents do not give carbonyl compounds with :

Identify the compounds $A$,$B$,and $C$ in the following reaction sequence:
$CH_3-Br$ $\xrightarrow{Mg, \text{Ether}} [A]$ $\xrightarrow[(ii) \text{Water}]{(i) CO_2} [B]$ $\xrightarrow{CH_3OH, H^+} [C]$

Which is most reactive towards soda-lime decarboxylation?

Oxalic acid reacts with concentrated $H_2SO_4$ to produce a mixture of two gases. When this mixture is passed through caustic potash,one of the gases is absorbed. What substance is formed by the absorption of the gas in caustic potash?