Consider the following options and their relation with alkali metals:
1) Size - The size of an atom decreases from left to right along a period, but noble gases have larger radii when compared to alkali metals.
2) Ionization energy - Alkali metals possess one valence electron in their outermost shell. If they were to lose this electron, they can attain noble gas configuration. Hence, the ionization energy is the lowest.
3) Alkali metals are highly electropositive.