Question

What is the colour of the precipitate formed by the addition of KI to Pb salt in water?
(A) Yellow
(B) Black
(C) White
(D) Red

Answer 1

$\text{Pb}{{\left( \text{N}{{\text{o}}_{3}} \right)}_{2}}+2\text{KI}\to \text{Pb}{{\text{I}}_{2}}+2\text{KN}{{\text{o}}_{3}}$ reaction. Potassium metal is soft and white with a silver luster, has a low melting point, and is a good conductor of heat and electricity. Potassium imparts a vapour that is green.

Complete step by step Solution
$\begin{aligned} & \text{Pb}{{\left( \text{N}{{\text{o}}_{3}} \right)}_{2}}+2\text{KI}\to \text{Pb}{{\text{I}}_{2}}+2\text{KN}{{\text{o}}_{3}} \\\ & \\\ \end{aligned}$
Where $\text{Pb}{{\text{I}}_{2}}$ precipitate is yellow
The reaction between Pb and KI results in the formation of $\text{Pb}{{\text{I}}_{2}}$ , which is yellow in colour.
So option A is correct answer.

Additional information
Phosphorus is a chemical element with the symbol P and atomic number15. Elemental phosphorus exists in two major forms, white phosphorus and red phosphorus, but because it is highly reactive, phosphorus is never found as a free element on Earth.
Potassium metal is soft and white with a silver luster, has a low melting point, and is a good conductor of heat and electricity. Potassium imparts a vapour that is green.
Iodine is a chemical element with the symbol I and atomic number 53. The heaviest of the stable halogens, it exists as a lustrous, purple black non-metallic solid at standard conditions that melts to form a deep violet liquid at 114 degrees Celsius and boils to a violet gas at 184 degrees Celsius.

Note
Double displacement reaction
As positive and negative radicals exchanged
$\text{P}{{\text{b}}^{+2}}\text{No}_{3}^{-1}2{{\text{k}}^{+1}}2{{\text{I}}^{-1}}\to \text{Pb}{{\text{I}}_{2}}+2\text{KN}{{\text{o}}_{3}}$
$\begin{aligned} & \text{Cr(OH}{{\text{)}}_{3}}=\text{ Green} \\\ & \\\ \end{aligned}$
$\text{Fe(OH}{{\text{)}}_{2}}=\text{Green}$
$\text{Fe(OH}{{\text{)}}_{3}}=\text{Brown}$
$\text{Zn}{{\left( \text{OH} \right)}_{2}}=\text{ White}$
AgBr = yellow
Agl = yellow
Precipitates are insoluble ionic solid products of a reaction, formed when certain cations and anions combine in an aqueous solution .The determining factors of the formation of a precipitate can vary.
The insoluble salt that falls out of solution is known as the precipitate, hence the reaction name.