Identify the reagent R used in following reaction?
Show Hint
Whenever you see a hydrogen atom on a saturated alkane chain being cleanly replaced by a halogen atom, look for molecular halogen paired with light energy ($\text{h}\nu$ or UV light) to trigger that free-radical path!
Step 1: Spot the reaction type.
A single H on a saturated carbon is swapped for a bromine. That is free radical substitution, not addition.
Step 2: Choose the reagent.
Bromine with UV light splits into bromine radicals that pull off a hydrogen and put bromine in its place. HBr would add across a double bond instead.
Step 3: Conclude.
The right reagent is $Br_2$ with UV light.
\[ \boxed{Br_2/\text{UV light},\ \text{option 4}} \]
