Meaning: 'Universe' refers to all of space and everything in it, including stars, planets, and all forms of matter and energy.

Wrong options:

• placement: Placement refers to the act of putting something in a particular position, which does not fit the context of discussing the composition of the world.
• subject: Subject typically refers to a topic or area of study, which is too narrow and does not capture the vastness implied in the context of alchemy.
• application: Application refers to the act of putting something into operation or use, which does not relate to the fundamental nature of existence as described in the sentence.

Correct answer: pure

Explanation: The word 'pure' is an adjective that describes a substance that is not mixed with anything else, fitting grammatically and contextually as it contrasts with the idea of different substances having varying qualities.

Meaning: 'Pure' means free from any contamination or mixture, indicating that walnut oil could be considered as untainted as silver in the alchemical context.

Wrong options:

• secure: Secure means safe or protected, which does not relate to the quality of a substance in the context of alchemy.
• allure: Allure refers to the quality of being attractive or charming, which is irrelevant to the discussion of substance quality.
• procure: Procure means to obtain something, which does not fit the context of describing the inherent qualities of substances.

Correct answer: scientists

Explanation: The term 'scientists' is a noun that refers to individuals who study or practice science, fitting grammatically and contextually as it contrasts the alchemists' views with modern scientific understanding.

Meaning: 'Scientists' are people who conduct scientific research to advance knowledge in an area of study, particularly in the natural and physical sciences.

Wrong options:

• people: People is a general term for humans and does not specifically relate to the context of scientific inquiry or knowledge.
• gadgets: Gadgets refer to small mechanical or electronic devices, which are not relevant to the discussion of scientific understanding.
• technology: Technology refers to the application of scientific knowledge for practical purposes, which does not specifically address the individuals conducting the research.

Correct answer: possible

Explanation: The word 'possible' is an adjective that indicates something can occur or be done, fitting grammatically and contextually as it questions the feasibility of distinguishing elements from compounds without atomic knowledge.

Meaning: 'Possible' means capable of happening or being done, indicating that without atomic knowledge, it would be challenging to differentiate between elements and compounds.

Wrong options:

• given: Given is a past participle that implies something has been provided, which does not fit the context of questioning the ability to distinguish substances.
• understood: Understood is a past participle that implies comprehension, which does not align with the inquiry about the ability to tell elements from compounds.
• stopped: Stopped is a past participle that indicates something has come to an end, which does not relate to the ability to identify substances.