what property of the noble gases most likely prevented the gases from being readily/easily discovered?

These gases very rarely react, with others and also noble gases are odourless and colourless.

Explanation:

Noble gases will not react with anything so that is the reason why they are known as an inert gas. Noble gases are present in group 18 on the periodic table and following the rule of the octet which is they completed their orbital by s2p6 which is the highest energy level. Most elements are discovering through their reactivity with the other elements, commonly with oxygen. In the case of a noble gas, it is difficult for a scientist to work with the gases which have very less or no chemical property in terms of their reactivity.