The reaction of methane with halogens like bromine ($\text{Br}_2$) in the presence of ultraviolet light ($h\nu$) or at high temperature is a free radical substitution reaction . The mechanism involves three steps: initiation (homolysis of the $\text{Br-Br}$ bond to generate free radicals), propagation, and termination .

• Benzene with $\text{Br}_2/\text{AlCl}_3$: This is an electrophilic substitution reaction where $\text{AlCl}_3$ acts as a Lewis acid catalyst to generate the electrophile ($\text{Br}^+$) .
• Acetylene with $\text{HBr}$: This is an electrophilic addition reaction across the triple bond .
• Propene with $\text{HBr}/(\text{C}_6\text{H}_5\text{COO})_2$: This is a free radical addition reaction, also known as the peroxide effect or anti-Markovnikov addition .