The compound formed by the reaction of ethanal with semicarbazide contains $.....................$ number of nitrogen atoms.

$Ph-CH_3$ $\xrightarrow{CrO_2Cl_2} (A)$ $\xrightarrow{conc. KOH} Ph-CH_2OH + (B)$
Product $(B)$ of the above reaction is:

$2-$pentanone can be distinguished from $3-$pentanone by the reagent:

An ester $(A)$ with molecular formula $C_9H_{10}O_2$ was treated with excess of $CH_3MgBr$ and the complex so formed was treated with $H_2SO_4$ to give an olefin $(B)$. Ozonolysis of $(B)$ gave a ketone with molecular formula $C_8H_8O$ which shows positive iodoform test. The structure of $(A)$ is

Acetal is obtained by reacting which of the following in the presence of dry $HCl$ and alcohol?

Which of the following can be used to convert $3$-methylbutan-$2$-one into isopentane?