Electronegativity is a measure of an element's ability to attract electrons. The more electronegative an element is, the more it attracts electrons. Bromine is more electronegative than astatine, which means that it attracts electrons more strongly. This makes bromine more reactive than astatine.
Atomic size is another factor that affects reactivity. The larger the atomic size, the less reactive the element. Astatine has a larger atomic size than bromine, which means that it is less reactive than bromine.
Therefore, bromine is more reactive than astatine due to its higher electronegativity and smaller atomic size.
