Question

A white salt soluble in $N{H_4}OH$ but insoluble in water is
A. $BaS{O_4}$
B. $CuS{O_4}$
C. $PbS{O_4}$
D. $AgCl$

Answer 1

A salt which forms a soluble complex with the ammonium hydroxide solution and does not get dissolved in water will be silver chloride. Those salts which form the complexes are generally soluble as they get dissociated in the solvent along with reacting with it immediately.

Complete step by step answer:
Whenever $AgCl$ is added to $N{H_4}OH$, it starts reacting with the solvent to form a soluble complex. The white colored salt shows the following reaction with $N{H_4}OH$:
$AgCl + 2N{H_4}OH \to [Ag(N{H_3}\mathop )\nolimits_2 ]Cl + 2{H_2}O$
The product that is formed along with the water is the soluble complex present in the solution. But, as soon as the $AgCl$ is added to water, it settles down to the bottom and does not get dissolved in the solvent. This is so because the lattice energy of the covalent compound $AgCl$ is much higher than the hydration/ solvation energy. Thus, placing the salt in water will show no reaction as there will be no bond cleavage and new bond formation among the free ions present in the water. This is the reason why we state that whenever the salt $AgCl$ is added into water, it remains insoluble.
Hence, the correct option of the question is (D) $AgCl$.

Note:
We need to understand that whenever salts like $AgCl$ are dissolved in water, the hydration energy is too low than the lattice energy of the salt and thus, it cannot get dissolved in the water.