An unsaturated hydrocarbon $\text{'}\mathrm{X}\text{'}$gives white precipitate with Tollen's reagent. If $\mathrm{X}$ is gaseous in nature, the molecular formula of $\mathrm{X}$ is

Tollen's reagent consists of a solution of silver nitrate and ammonia.

Terminal alkynes react with tollen's reagent and form white color precipitate.

With Tollen's reagent (ammoniacal ${\mathrm{AgNO}}_3$), a white precipitate of silver salt is obtained.

$\mathrm{H}-\mathrm{C}\equiv \mathrm{C}-\mathrm{H}+2{\mathrm{AgNO}}_3+2{\mathrm{NH}}_4\mathrm{OH}\to \underset{\mathrm{Sliver} \mathrm{acetylide} (\mathrm{white} \mathrm{ppt}.)}{\mathrm{Ag}-\mathrm{C}\equiv \mathrm{C}-\mathrm{Ag}}+2{\mathrm{NH}}_4{\mathrm{NO}}_3+{\mathrm{H}}_2\mathrm{O}$