Which functional group having two carbon atoms does not give a compound?

Which of the following compounds has a sweet,fruity smell?

What will you observe on adding a $5\%$ alkaline potassium permanganate solution drop by drop to some warm ethanol taken in a test tube? Write the name of the compound formed during the above chemical reaction.

$(a)$ Give chemical tests to detect the presence of:
$(i)$ Ethanol
$(ii)$ Ethanoic acid
$(b)$ Why is ethanoic acid called glacial acetic acid?

What is the monomer unit of neoprene?

$A$ compound $C$ (molecular formula $C_2H_4O_2$) reacts with $Na$ metal to form a compound $R$ and evolves a gas which burns with a pop sound. Compound $C$ on treatment with an alcohol $A$ in the presence of an acid forms a sweet-smelling compound $S$ (molecular formula $C_3H_6O_2$). On addition of $NaOH$ to $C$,it also gives $R$ and water. $S$ on treatment with $NaOH$ solution gives back $R$ and $A$. Identify $C$,$R$,$A$,$S$ and write down the reactions involved.