Specify why the noble gases were among the last naturally occurring elements to be discovered.

Inert Nature: Noble gases are the elements that belong to the Group 18 of the periodic table. They are helium, neon, argon, krypton, xenon, and radon. These gases are known for their low reactivity or inertness. This means they do not readily combine with other elements to form compounds. This characteristic made them difficult to detect.

Presence in the Atmosphere: Noble gases are present in very small quantities in the Earth's atmosphere. For example, argon is the most abundant noble gas, making up approximately 0.93% of the Earth's atmosphere. The other noble gases are present in even smaller quantities. This made their detection and isolation even more challenging.

Lack of Spectral Lines: Before the invention of modern detection equipment, elements were often discovered through their spectral lines - the specific wavelengths of light that an element emits or absorbs. However, noble gases do not easily emit energy and thus do not produce strong spectral lines. This made them difficult to discover using the technology available at the time.

Advanced Detection Methods: The discovery of noble gases required more advanced detection methods. For example, helium was first discovered in the sun's spectrum before it was found on Earth. Argon was discovered when scientists isolated it from the air. These advanced methods were not developed until the late 19th and early 20th centuries, which is why noble gases were among the last naturally occurring elements to be discovered.