Final answer:
Halogens have the most negative electron affinities because they have one electron less than a neighboring noble gas, making them highly reactive and eager to accept an extra electron to achieve stability.
Step-by-step explanation:
The elements with the most negative electron affinities are the halogens. Halogens, belonging to Group 17 (Group VII) of the periodic table, are highly reactive and readily accept an extra electron due to having one vacancy in their outermost p subshell. This electron acceptance results in the formation of stable, singly negative ions. In contrast, alkali metals and alkaline earth metals tend to lose their outermost electrons, becoming positively charged ions. Therefore, the correct answer to which elements have the most negative electron affinities is b. halogens.