NEET Practice Questions (MCQs) with Answers & Solutions

$BaSO_4$ (Barium sulfate) is insoluble in water. This is due to the low solubility product (Ksp) of barium sulfate, which makes it precipitate out of solution rather than dissolve.

Cobalt chloride in its hydrated form is pink. When cobalt chloride absorbs water, it forms a complex that gives a pink color. This property is often used in humidity indicators.

Nessler’s reagent is a chemical reagent used to detect ammonia ($NH_4^+$) in aqueous solutions. When ammonia is present, Nessler's reagent produces a yellow to brown color, indicating the presence of $NH_4^+$. This reaction is due to the formation of a colored complex.

The reagents $NH_4Cl$ (ammonium chloride) and aqueous $NH_3$ (ammonia) are used to precipitate $Al^{3+}$ (aluminum ions) from a solution. This is because $Al^{3+}$ forms a white precipitate of $Al(OH)_3$ (aluminum hydroxide) in the presence of ammonia and ammonium chloride. The reaction is as follows: $Al^{3+} + 3NH_3 + 3H_2O ightarrow Al(OH)_3 ext{(s)} + 3NH_4^+$.

Hemoglobin is a complex protein that contains an iron ion in its heme group. The iron ion in hemoglobin is in the ferrous state, which is $Fe^{2+}$. This allows hemoglobin to bind oxygen molecules for transport in the bloodstream. The presence of $Fe^{2+}$ is crucial for the oxygen-binding capability of hemoglobin.

Nessler's reagent is used for the detection of ammonia, and the active species in Nessler's reagent is $ HgI_4^{2-} $. This species reacts with ammonia to form a brown precipitate or coloration, which is indicative of the presence of ammonia.

Among the given sulphides, CdS (Cadmium Sulphide) is only completely precipitated when the acidic solution is made dilute. This is because CdS has a low solubility product (Ksp), and in a highly acidic medium, the concentration of hydrogen ions (H+) is too high, which prevents complete precipitation of CdS.