Which two groups of elements in the periodic table are considered the most reactive?

• A. Alkali metals (Group 1) and halogens (Group 17)
• B. Transition metals (Groups 3-12) and lanthanides
• C. Metalloids and actinides
• D. Noble gases (Group 18) and alkaline earth metals (Group 2)

Answer: (A)

Verified step by step guidance

1. Understand that reactivity in the periodic table depends on how easily elements lose or gain electrons to achieve a stable electron configuration.
2. Recognize that Group 1 elements, known as alkali metals, have a single electron in their outermost shell, which they tend to lose easily, making them highly reactive.
3. Know that Group 17 elements, called halogens, have seven electrons in their outermost shell and tend to gain one electron to complete their octet, making them very reactive as well.
4. Compare these groups to others: transition metals (Groups 3-12) and lanthanides are less reactive due to their electron configurations and multiple oxidation states; metalloids and actinides have varied reactivities but are generally not the most reactive groups; noble gases (Group 18) are very stable and unreactive, and alkaline earth metals (Group 2) are reactive but less so than alkali metals.
5. Conclude that the two most reactive groups are alkali metals (Group 1) and halogens (Group 17) because of their strong tendencies to lose or gain electrons, respectively.