Which of the following compounds yields propanone upon dehydrogenation?

The reaction of $4-(\text{aminomethyl})\text{cyclohexylmethanol}$ with acetic anhydride $(Ac_2O)$ proceeds in two steps to form $P$ and $Q$. Identify $P$ and $Q$ respectively.

How is the presence of $C_2H_5OH$ in $CH_3OH$ determined?

Identify the final product in the following reaction sequence: $CH \equiv CH$ $\xrightarrow[H_2SO_4]{HgSO_4}$ $\xrightarrow[H_2O]{CH_3MgBr}$ $\xrightarrow{P/Br_2}$

Treatment of a $2^{\circ} \text{ alcohol}$ with $CrO_3/H_2SO_4$ yields a/an

When wine is exposed to air,it becomes sour. The reason for this is -