The activity series shows the order of reactivity of elements. The reaction Br2 + NaF -----> does not occur because bromine is less than fluorine in the activity series.
The activity series shows the order of reactivity of elements. The elements that are higher in the activity series will displace the elements that are lower in the activity series.
The activity series of halogens is shown as; F > Cl > Br > I. Let us consider the reaction; Br2 + NaF ----->
We can see that bromine is less than fluorine in the activity series hence there will be no reaction because bromine can not not displace fluorine.