Question

An unknown compound (A) has a molecular formula $C_4{H}_6.$ When (A) is treated with excess of $B{r}_2/CC{l}_4$ a new compound (B) with formula $C_4{H}_{6}B{r}_4$ is formed. (A) forms a white ppt. with ammonical silver nitrate solution. The compound (A) is :

• A. But-1-yne
• B. But-2-yne
• C. But-1-ene
• D. But-2-ene

Answer 1

The correct option is A But-1-yne

The formula is $C_4{H}_6.$ It corresponds to alkyne ( $C_4{H}_{2\left(4\right)-2})$ i.e. Butyne.
It is confirmed by the fact that it gives addition reaction with excess $B{r}_2$ and gets converted into $\left(C_4{H}_{6}B{r}_4\right)$
Now Butyne can be 1-butyne or 2-butyne
But only terminal alkyne can react with Tollens reagent (i.e., with ammonical $AgN{O}_3$ solution) to form white precipitate as they have acidic proton.
Hence the compound is But-1-yne.