Arrange the following hydrogen halides in order of their decreasing reactivity with propene.
(i) HCl > HBr > HI
(ii) HBr > HI > HCl
(iii) HI > HBr > HCl
(iv) HCl > HI > HBr
The answer is the option (iii) HI > HBr > HCl
Explanation: The factors that affect the reactivity of hydrogen halides are bond strength and bond dissociation energy. We know that, in halogen halides the size of the halogen atom increases, the bond dissociation energy, as well as bond strength, decreases.
Hence, the option (iii) is the correct order.