Which element is classified as a noble gas? o, n,cl, xe?

Xe

Explanation:

Noble gas are the elements which have their valence shell complete and are almost inert in nature. They have very low reactivity and they exist in gaseous form.

The electronic configuration of oxygen is:-

The electronic configuration of nitrogen is:-

The electronic configuration of chlorine is:-

The electronic configuration of xenon is:-

Since, Xenon has its valence electron having 8 electrons and thus, it is a noble gas.

considering the question as per the attachment

here we can see that the radon nuclide has 222 as the atomic mass number and 86 as the atomic number.

when it undergoes nuclear fission it gives polonium which has atomic mass number as 218 and atomic number will be 84 along with a helium nucleus which has 4 atomic mass number and 2 as its atomic number.

222 = 218 + 4 (atomic mass number)

86 = ? + 2; therefore ? = 86-2 = 84.

the atomic mass number of polonium will be 84.