WBCS Preliminary Examination 2023 — General Studies · Question 87 of 200

Answer: (B) Yellow precipitation of lead iodide is formed.

$Pb(NO_3)_2 + 2KI \rightarrow PbI_2\downarrow + 2KNO_3$. This is a double displacement (precipitation) reaction in which insoluble lead iodide separates as a bright yellow precipitate, while potassium nitrate stays in solution. Colours of other common precipitates: $BaSO_4$ and $AgCl$ are white, $AgBr$ is pale yellow, $AgI$ is yellow, $Cu(OH)_2$ is blue, $Fe(OH)_3$ is reddish-brown, and $PbS$ and $CuS$ are black. White, red and black are therefore all wrong for lead iodide.