Question

What is the smell of hydrogen sulphide at a concentration of 200 pm?
A. Pleasant odor
B. Rotten egg odor
C. No smell
D. Rotten fish smell

Answer 1

Hint: Hydrogen sulfide is generally a colorless gas represented by molecular formula ${{H}_{2}}S$. Hydrogen sulfide has density slightly higher than air and it is generally explosive in nature which burns in oxygen with blue flame.

Complete answer:
Hydrogen sulfide generally acts as a reducing agent especially in the presence of base and forms compounds having negative charge known as $S{{H}^{-}}$ion. It is poisonous, corrosive and flammable gas. It has a smell of rotten eggs. Hydrogen sulfide is generally produced by the microbial breakdown of organic matter in the absence of oxygen gas like in swamps and sewers and this process is commonly known as anaerobic digestion which is done by sulfate reducing microorganisms. Hydrogen sulfide gas also occurs in volcanic gases and natural gas.
Hydrogen sulfide is slightly soluble in water and it acts as a weak acid. Hydrogen sulfide and its solutions are colorless. When these are exposed to air it slowly oxidizes to form elemental sulfur and this is not soluble in water and ${{H}_{2}}S$reacts with metal ion it forms metal sulfides which are insoluble and form dark colored solids.
Hence from the above discussion we conclude that hydrogen sulphide at a concentration of 200 pm has the smell of rotten egg.

Option B is true.

Note:
The main use of hydrogen sulfide is it used as a precursor to elemental sulfur. Many organosulfur compounds are produced by starting product hydrogen sulfide. These include methanethiol, ethanethiol, thioglycolic acid etc.