CBSE Class 10 Answered

The first person to actually isolate and note the presence of these noble gases was Henry Cavendish.

He removed all the nitrogen and oxygen chemically from a receptacle containing air. The nitrogen was oxidised to NO₂ by electric discharges and absorbed by a sodium hydroxide solution. Remaining oxygen was removed from the mixture by a special adsorber. 1/120 of the gas volume remained unreacted in the receptacle. As we know today, this must have been mainly argon (99.8%) and traces (0.2%) of other noble gases.

Two reasons for late discoveries of noble gases are:

1. They are present in extremely low concentrations in our environment.

2. They are very inert.