Question

The reagent with which an alkene must react so that the colour of the solution changes from orange to colourless is :

• A. $B{r}_2$ in presence of $CC{l}_4$
• B. $Zndust$
• C. $NaOH/CaO$
• D. All of the above.

Answer 1

The correct option is A $B{r}_2$ in presence of $CC{l}_4$

This is a confirmatory test of alkenes or the test of unsaturation.
When an alkene is mixed with bromine in $CC{l}_4$ its colour changes from orange to colorless. Bromine in $CC{l}_4$ is a orange brown coloured solution. When bromine reacts with alkene it forms dibromoalkane by addition reaction, due to which orange colour disappears.
Example: $R-C{H}_2=C{H}_2-R+B{r}_2\stackrel{CC{l}_4}{⟶}R-C{H}_{2}Br-C{H}_{2}Br-R$