JEE Advanced 2015 · Paper 1, Chemistry question 31

Protonation. H⁺ adds to C1 of isoprene, giving the tertiary allylic cation $\ce{(CH3)2C+-CH=CH2 <-> (CH3)2C=CH-CH2+}$.

Bromide attack. At the primary end (1,4-addition), it gives the more substituted, thermodynamically favoured alkene: $\ce{(CH3)2C=CH-CH2Br}$.

(D)