Step 1: Concept Alkyl fluorides are prepared by heating alkyl chlorides or bromides in the presence of metallic fluorides like $AgF$, known as the Swarts reaction.
Step 2: Meaning Tert-butyl bromide is a tertiary alkyl halide, and $AgF$ acts as the fluorinating agent.
Step 3: Analysis The bromine atom in $(CH_3)_3C-Br$ is substituted by a fluorine atom to form $(CH_3)_3C-F$.
Step 4: Conclusion The IUPAC name for $(CH_3)_3C-F$ is 2-fluoro-2-methylpropane.
Final Answer: (B)