Which gas is both colorless and odorless?

Argon, carbon dioxide, carbon monoxide, nitrogen and neon.

The gas that is both colorless and odorless is Argon. It is a gas symbolized by Ar in the periodic table of elements. It has an atomic number of 18 and is found in group 18 in the periodic table. It is the 3rd most common gas in the Earth's atmosphere. It also makes up most of the noble gasses in the Earth's crust. The word argon is derived from a greek word which means lazy or inactive. This is because the element undergoes almost no chemical reactions. There is a complete octet (eight electrons) forming Argon's shell which makes it stable and impenetrable to bonding with other elements.