1. Write the name of side substituent according to the alphabetical order. Example: bromo is written before chloro as B comes before C.

2. Always use a hyphen {-} between a number and a alphabet. Since Br is attached to 2 position and Cl is attached to third position i.e. it is written as 2-Bromo and 3-chloro.

3. Lastly, write the name of the longest hydrocarbon chain i.e. butane of 4 carbons.