The molecular formula of the first member of the family of alkenynes and its name is given by the set:

Ethene can be separated from acetylene by passing the mixture through :

At low temperatures,the slow addition of molecular bromine to $CH_2=CH-CH_2-C \equiv CH$ gives:

Which of the following reagents is most suitable to distinguish compound $(3)$ from the others?
$(1) \ CH_3-C \equiv C-CH_3$
$(2) \ CH_3CH_2CH_2CH_3$
$(3) \ CH_3CH_2C \equiv CH$
$(4) \ CH_3CH=CH_2$

The product $(K)$ of the following reaction is:

$A$ hydrocarbon $X$ with molecular formula $C_4H_6$ decolourises bromine water and forms a white precipitate in ethanolic $AgNO_3$ solution. Treatment of $X$ with $HgCl_2$ in aqueous $H_2SO_4$ produces a compound,which gives a yellow precipitate when treated with $I_2$ and $NaOH$. The structure of $X$ is