Question

An unknown compound A has a molecular formula C₄H₆. When A is treated with excess of Br₂ a new substance B with formula C₄H₆Br₄ is formed. A forms a white ppt. with ammonical silver nitrate solution. A may be 

(a) but-1-yne 

(b) but-2-yne

(c) but-1-ene

(d) but-2-ene 

Answer 1

(a) but-1-yne 

The formula is C_4​H₆​. It corresponds to alkyne (i.e. C₄​H_2(4)−2​). i.e. Butyne.

It is confirmed by the fact that it gives addition reaction with excess Br_2​ and gets converted into (C₄​H₆​Br₄​)

Now Butyne can be 1-butyne or 2-butyne

But only terminal alkyne reacts with Tollens reagent as they have acidic proton. (i.e. with ammonical AgNO₃​) solution.

Hence the compound is But-1-yne.