Henry Cavendish's Famous Discovery in 1766

The question asks about a significant discovery made by the English scientist Henry Cavendish in the year 1766. Cavendish was a brilliant natural philosopher known for his precise measurements and experiments.

In 1766, Henry Cavendish conducted a series of experiments studying "inflammable air," a gas produced when certain metals, like zinc or iron, react with acids. Although "inflammable air" had been observed before, Cavendish was the first to collect it, study its properties systematically, and recognize it as a distinct substance different from ordinary air or other known gases.

He noted that this "inflammable air" was much less dense than air and that it burned with a pale flame, producing water. This observation that burning "inflammable air" produced water was a crucial finding, although the full significance of this reaction involving oxygen (from air) was later explained by Antoine Lavoisier.

Cavendish is credited with identifying "inflammable air" as a unique element, which was later named "hydrogen" by Lavoisier, meaning "water-former." Therefore, his key discovery in 1766 was hydrogen.

Analyzing the Options and Discoveries

Let's look at the other options provided and their historical context regarding discovery dates and discoverers:

• Oxygen: Discovered independently by Carl Wilhelm Scheele around 1772 (published 1777) and Joseph Priestley in 1774.
• Hydrogen: Isolated and characterized as a distinct element by Henry Cavendish in 1766.
• Helium: First detected spectrographically in the Sun in 1868 by Pierre Janssen and Norman Lockyer, and isolated on Earth in 1895 by William Ramsay.
• Chlorine: Discovered by Carl Wilhelm Scheele in 1774.

Comparing the dates, only hydrogen was discovered by Henry Cavendish in 1766, matching the information in the question.

Conclusion on Cavendish's 1766 Discovery

Based on historical records of scientific discoveries, Henry Cavendish's major contribution in 1766 was his work on "inflammable air," which led to the identification of hydrogen as a unique chemical element.

Revision Table: Key Facts

Additional Information about Henry Cavendish and Hydrogen

Henry Cavendish was a reclusive but highly influential scientist. Besides his work on gases, he is also famous for the Cavendish experiment in 1798, where he measured the density of the Earth. This experiment effectively determined the gravitational constant 'G'.

Hydrogen (\(\text{H}_2\)) is the lightest element on the periodic table. It is the most abundant chemical substance in the universe, found primarily in stars and gas giant planets. On Earth, it is rarely found in its pure elemental form and is usually combined with other elements, most notably in water (\(\text{H}_2\text{O}\)).