Q.Which of the following compounds does not produce a white precipitate on treatment with ammoniacal silver nitrate solution?

Only a terminal alkyne (one with a $\equiv C\text{-}H$) can form a silver acetylide precipitate with ammoniacal $AgNO_3$; an internally-substituted (non-terminal) alkyne cannot.

Ammoniacal silver nitrate reacts specifically with terminal alkynes (alkynes with a $\equiv C\text{-}H$ at the end of the chain), because the triple-bond hydrogen is weakly acidic and is displaced by $Ag^+$, forming an insoluble white/grey silver acetylide precipitate:

$R\text{-}C\equiv CH + [Ag(NH_3)_2]^+ \rightarrow R\text{-}C\equiv C\text{-}Ag\downarrow + NH_3 + NH_4^+$

Check each option:

• Acetylene, $HC\equiv CH$ — terminal on both ends → gives precipitate.
• Methyl acetylene, $CH_3\text{-}C\equiv CH$ — terminal → gives precipitate. …