In the presence of dil. $HCl$,compound $A$ is converted to a constitutional isomer $(B)$. Compound $B$ is:

Which of the following reactions will give $\alpha$-hydroxy acid as a product?

Statement-$I$ :- Acetaldehyde and acetone can be distinguished by Tollen's reagent.
Statement-$II$ :- Aromatic aldehyde does not give Fehling test.

An aromatic compound $A$ (Molecular formula $C_{8}H_{8}O$) gives a positive $2,4-DNP$ test. It gives a yellow precipitate of compound $B$ on treatment with iodine and sodium hydroxide solution. Compound $A$ does not give Tollen's or Fehling's test. On drastic oxidation with potassium permanganate,it forms a carboxylic acid $C$ (Molecular formula $C_{7}H_{6}O_{2}$),which is also formed along with the yellow compound in the above reaction. Identify $A, B$ and $C$ and write all the reactions involved.

Which of the following reactions is preferentially used to prepare the corresponding alkanes from alkanones?

What is the product formed when acetaldehyde reacts with $PCl_5$?