Question

An unknown compound ( A) has a molecular formula C₄ H₆. When (A) is treated with excess of Br₂ a new substance (B) with formula C₄H₆ Br₄ is formed. (A) forms a white ppt. with ammoniacal silver nitrate. Compound A is

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

Answer 1

The correct option is A

(a)But-1-yne

A is $C_4{H}_6$

Degree of unsaturation

= No of carbon atoms $+1-\frac{1}{2}$ {No of H atoms + No of halogen atoms - No of Nitrogen atoms}

$=4+1-\frac{6}{2}$

$=5-3=2$

Ammoniacal $AgN{O}_3$ is Tollen's reagent.
Terminal alkynes

$R-C\equiv CH\stackrel{AgN{O}_3/N{H}_3}{\to }R-C\equiv CAg\downarrow$
$\left(Whiteppt\right)$

Given compound is a terminal Alkynes.
So only option (A) is appropriate.