What are two reasons that the noble gases had escaped notice?

Noble gases are also called as inert gases.

Explanation:

These gases make up the chemical elements with similar properties under standard conditions, they are color odorless and have very low chemical reactivity. These gases are Krypto, Helium, neon and Argon and Xenon and Radon, etc. Having weaker interatomic forces, they have a low boiling and heating points. Being lighter these gas tend to have escaped from the atmosphere of the earth at the formation of the planet as the blowing of solar winds. Another reason that thee gases are being unstable and various compounds like chlorine, gold, mercury, and xenon contain these noble gases and hence are numerous and released mixed with light or heat they escape into space.

Icant see the pictures 

Compound with sulfer  is bright red