Question

All noble gases are
(A) colourful
(B) colourless and odourless
(C) colourless and but have odour
(D) none of these

Answer 1

Hint: Symmetry and exchange energy are the causes for the greater equilibrium of atoms with half-filled or totally filled orbitals. - We realise that half-filled or completely filled atomic orbitals have more symmetry than any other electronic structure, which adds to the atom's increased stability.

Complete answer:
The noble gases (historically known as inert gases; also known as aerogenes[1]) are a group of chemical elements with identical properties; they are all odourless, colourless, monatomic gases of very low chemical reactivity under normal conditions. Helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and nuclear radon are the six naturally occurring noble gases (Rn). Oganesson (Og) has been speculated to be a noble gas or to defy the trend due to relativistic effects; however, its composition has yet to be studied.
Under normal conditions, noble gases are colourless, odourless, tasteless, and nonflammable.
The noble gases are grouped in the periodic table according to their boiling point.
Noble gases are used in a variety of applications, ranging from incandescent lamps to excimer lasers.
Xenon is used as an anaesthetic because of its high lipid solubility, which makes it more active than nitrous oxide and because it is quickly eliminated from the bloodstream, allowing for quicker healing.
Via hyperpolarized MRI, xenon is used in medical imaging of the lungs.
In radiotherapy, radon is used, and is extremely radioactive and only present in trace quantities.
Hence option (B) is correct.

Note:
The properties of noble gases are well explained by contemporary atomic structure theories. Noble gases have a "full" outer shell of valence electrons, which makes them less likely to engage in chemical reactions. Just a few hundred noble gas compounds have been prepared so far. For eg, both the n = 1 and n = 2 shells of Neon (Ne) are complete, making it a stable monatomic gas under atmospheric conditions.