Hint: Reactivity of an acid is inversely proportional to the bond energy.
 
Explanation:
The order of reactivity parallels the order of acidity. The stronger the acid, the more readily it provides H⁺ ions for addition to the double bond. The stability of hydrogen halides decreases down the group due to decrease in bond (H−X) dissociation energy in the order:  HI > HBr > HCl.

Bond energy of HI is 296.8 kJ/mol, HBr is 362.7 kJ/mol and HCl is 430.5 kJ/mol. As bond energy decreases the reactivity of hydrogen halide compound increases. In the case of hydrogen halide, down the group reactivity increases with propene. 

Hence, HI > HBr > HCl is the order of reactivity with propene. So, option 3 is the correct answer.