Final answer:
The lightest members of the alkali metals, alkaline earth metals, halogens, and noble gases are lithium, beryllium, fluorine, and helium respectively, based on their atomic numbers.
Step-by-step explanation:
Using the periodic table, we can identify the lightest member of each of the following groups:
- (a) Alkali metals: The lightest alkali metal is lithium (Li) with an atomic number of 3.
- (b) Alkaline earth metals: The lightest alkaline earth metal is beryllium (Be) with an atomic number of 4.
- (c) Halogens: The lightest halogen is fluorine (F) with an atomic number of 9.
- (d) Noble gases: The lightest noble gas is helium (He) with an atomic number of 2.