Final answer:
In the chemical reaction provided, there is one molecule of bromine (Br2) in the reactants. The oxidation numbers are 0 for the elemental forms (Na, Br2) and become +1 for Na+ and -1 for Br− after the reaction.
Step-by-step explanation:
The question refers to a chemical reaction where sodium fluoride (NaF) reacts with bromine (Br2) to form sodium bromide (NaBr) and fluorine (F2).
The question asks how many molecules of Br2 are present in the reactants. Since the molecular formula for bromine is written as Br2, it indicates that there is one molecule of bromine in the reactant.
Furthermore, the oxidation numbers for the atoms in this reaction may also be relevant. In elemental form, such as Na and Br2, the atoms have oxidation numbers of 0.
After the reaction, the resulting ionic products, Na+ ions and Br− ions, have oxidation numbers of +1 and −1, respectively.
To balance reactions involving halogens, it's important to note the reactivity of the halogen group (group 17), which decreases from top to bottom.
Fluorine is the most reactive, while iodine is the least. This is relevant in halogen replacement reactions where a more reactive halogen can replace a less reactive one.