What happen when ethene oxidised with cold KMnO4

Explanation

Order of reactivity of alkyl halide towords `SN^2` displacement follows the order `3^@ lt 2^@ lt 1^@`
In this case all the alkyl halides are 19, in such case the electrophilic carbon which is less sterically hindered will react faster. Hence order of reactivity is :
1-Bromo-2, 2-dimethylpropane <1- Bromo-2-methylbutane <1-Bromobutane.