Correct Answer: The chemist said that they did not have stock of that medicine then.

Solution : The fourth option is the correct choice.

The steps of conversion are as follows:

• There would be no change in the reporting verb in the indirect speech.
• "We" (a first-person pronoun) is changed to "they" (a third-person pronoun).
• The present tense "do not" is changed to the past tense "did not".
• "This" is changed to "that".
• The connector "that" is used to introduce the reported clause.

Therefore, the correct answer is: "The chemist said that they did not have stock of that medicine then."

Correct Answer: Marcellin Berthelot

Solution : The correct answer is Marcellin Berthelot

Marcellin Berthelot was a French chemist and politician known for his significant contributions to the field of chemistry. He was among the first scientists to successfully synthesise organic compounds, such as formic acid, methane, and acetylene, from their elemental components.

Correct Answer: Erich Huckel

Solution : The correct option is Erich Huckel.

German scientist and physicist Erich Huckel put up a theory in 1931 to assist in identifying whether an aromatic property would be present in a planar ring molecule. According to his rule, an aromatic, cyclic, planar molecule possesses 4n+2 electrons. Hückel's Rule is the name given to this principle.

Correct Answer: 63

Solution : The correct answer is 63.

The Russian chemist Mendeleev made the greatest contribution to the creation of the periodic table, which arranged the elements according to similar chemical properties as well as their atomic mass, a fundamental property. At the time, only 63 elements were known.

Correct Answer: Julius Lothar Meyer

Solution : The correct option is Julius Lothar Meyer.

The German chemist who first showed a graphical representation of the periodicity of an atomic volume plotted against atomic weight was Julius Lothar Meyer. Meyer, along with Dmitri Mendeleev, independently developed early versions of the periodic table in the 1860s. Meyer's work focused on plotting atomic volumes against atomic weights, and his graphical representation revealed periodic trends in properties, similar to Mendeleev's tabular arrangement.

Correct Answer: Alfred Werner

Solution : The correct option is Alfred Werner.

The first person to comprehend the molecular structures of inorganic substances, especially coordination compounds, was the Swiss chemist Alfred Werner in 1893. His groundbreaking work in coordination chemistry led to his proposal of the coordination theory, earning him the Nobel Prize in Chemistry in 1913.

Correct Answer: Hermann Kolbe

Solution : The correct option is Hermann Kolbe.

The German chemist who used the technique of preparing hydrocarbons by electrolysis of solutions of salts of fatty acids was Hermann Kolbe. He made significant contributions to the field of organic chemistry, and his work on electrolysis paved the way for the synthesis of organic compounds from inorganic precursors. This process, known as Kolbe electrolysis, demonstrated that organic molecules could be created from inorganic sources, challenging the then-prevailing theory of vitalism in chemistry.

Correct Answer: Hermann Kolbe

Solution : The correct answer is Hermann Kolbe.

In 1845, the German chemist Hermann Kolbe published a method for the synthesis of acetic acid, a natural product containing two carbon atoms. This work by Kolbe was a significant contribution to the understanding of organic chemistry and marked a key advancement in the synthesis of organic compounds.