Why are the elements of Group $18$ known as noble gases?

Given below are two statements:
Statement-$I$: Noble gases have very high boiling points.
Statement-$II$: Noble gases are monoatomic gases. They are held together by strong dispersion forces. Because of this,they are liquefied at very low temperatures. Hence,they have very high boiling points.
In the light of the above statements,choose the correct answer from the options given below:

Which of the following statements is correct?

Monazite is a source of

Which group of elements are all gases under normal conditions?

The reason for the noble gases to have low boiling and low melting points is: