Question

Which are not blackened by atmospheric ${H_2}S$ ?
A.$Ti{O_2}$
B.$ZnO$
C.$ZnS{O_4} + BaS$
D.All of these

Answer 1

To answer this question, you must recall the properties and reactions of hydrogen sulfide. Also we must be familiar with the properties of metal sulfides. Oxides form their respective sulphides on reaction with hydrogen sulphide.

Complete step by step solution:
Hydrogen sulfide is a poisonous and flammable naturally occurring gas. It is obtained as a product of the breakdown of organic matter like decomposing underground deposits and dead matter. Thus it is often present in wells drilled in sandstone and near coal mines and oil fields.
It is a pollutant in air and is corrosive in nature. Of the given compounds, both zinc sulphate and zinc oxide react with hydrogen sulphide in presence of ammonium hydroxide to form zinc sulphide. We know that zinc sulphide is a white coloured salt which on prolonged exposure to light turns yellow. Thus, it is not blackened. The reaction between zinc ion and hydrogen sulphide is given by
$Z{n^{2 + }} + {H_2}S \to ZnS$
Titanium dioxide also reacts with hydrogen sulphide but does not form a black precipitate. Thus, we can conclude that none of the compounds given in the question are blackened by hydrogen sulphide or in other words, all of these compounds are not blackened by atmospheric hydrogen sulphide.

Thus, the correct answer is D.

Note:
Atmospheric hydrogen sulphide under high humidity and moisture causes corrosion of a noble metal silver. When exposed to hydrogen sulfide, silver forms black coloured silver sulfide which makes a black coloured tarnish layer over the surface of silver hiding its natural lustre. We can say that silver is blackened by atmospheric hydrogen sulphide.