Which of the following is NOT a noble gas?

Hydrogen

The correct answer is option 2. Hydrogen.

Hydrogen \((H_2)\) is not a noble gas. It is a diatomic molecule and belongs to Group 1 of the periodic table. Noble gases, also known as inert gases, are a group of chemical elements in Group 18 of the periodic table. They are helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn). These gases are characterized by their low reactivity and full valence electron shells, making them stable and unreactive under normal conditions.