$CH_3CHO$ $\xrightarrow[5\,^{\circ}C]{10\%\,NaOH}$ $\xrightarrow[\Delta]{}$ $\xrightarrow[Ni]{H_2} (A)$; Product $(A)$ of the reaction is

Among the following compounds,which will give maximum enol content in solution?

Arrange the following compounds in decreasing order of reactivity towards nucleophilic addition reactions:
$(I) \ HCHO$,$(II) \ CH_3CHO$,$(III) \ CH_3COCH_3$,$(IV) \ CH_3CH_2COCH_2CH_3$

An organic compound $(X)$ with molecular formula $C_3H_6O$ is not readily oxidised. On reduction it gives $(C_3H_8O)$ $(Y)$ which reacts with $HBr$ to give a bromide $(Z)$ which is converted to a Grignard reagent. This Grignard reagent on reaction with $(X)$ followed by hydrolysis gives $2,3-$dimethylbutan$-2-$ol. Compounds $(X)$,$(Y)$ and $(Z)$ respectively are $:$

Geminal diols (compounds with two $-OH$ groups on the same carbon atom) are generally unstable. However,which of the following is stable?

The product $A$ in the above reaction is