The two groups of elements in the periodic table that are the most reactive are alkali metals and halogens.
- Alkali metals (found in Group 1) are highly reactive, particularly with water and halogens.
- Halogens (found in Group 17) are also very reactive, especially with alkali metals, as they tend to gain an electron to achieve a stable electron configuration.
The other groups mentioned:
- Noble gases are generally non-reactive due to their full valence electron shells.
- Alkaline earth metals (Group 2) are reactive but not as reactive as alkali metals.
Therefore, the correct answer is: alkali metals and halogens.